Contents

• The U.S.-South Korea Alliance and Congress's Role
• Military Forces in South Korea
• U.S. Forces Korea (USFK)
• United Nations Command (UNC)
• Combined Forces Command (CFC)
• South Korea's Defense Industry and Purchases of U.S. Weapon Systems
• Key Issues for Congress
• U.S. Troops Levels in South Korea
• "Strategic Flexibility": Alliance Coordination Off the Korean Peninsula
• Role of U.S. Forces in a Potential Conflict over Taiwan
• Role of ROK Forces in a Potential Conflict over Taiwan
• Congress, "Strategic Flexibility," and Taiwan
• Cost Sharing
• Chain of Command/Wartime Operational Control
• Delays and Reassessment of OPCON Transition Plan
• Debate Around OPCON Plan Implementation
• OPCON and the United Nations Command
• Extended Deterrence on the Korean Peninsula and South Korea's Nuclear Armament Debate
• Congress's Role in Extended Deterrence
• U.S.-ROK-Japan Trilateral Cooperation
• U.S.-South Korean Cooperation on Shipbuilding
• U.S.-ROK Alignment on North Korea

Summary

In the wake of the Korean War (1950-53), the United States and South Korea (officially the Republic of Korea, or ROK) forged an alliance that remains one of the United States' most significant military arrangements in Asia. Under the Mutual Defense Treaty that took effect in 1954, the United States and South Korea committed to defend each other against armed attack. Today, about 28,500 U.S. troops are stationed in South Korea. The alliance has traditionally focused on perceived threats from North Korea (officially the Democratic People's Republic of Korea, or DPRK), which have changed as North Korea has developed weapons of mass destruction (WMD) and missile capabilities. South Korea is included under the U.S. "nuclear umbrella," also known as extended deterrence.

Over the last few decades, the United States and South Korea have taken steps to reform the alliance. These steps unfolded as South Korea emerged as a wealthier country due to its rapid economic growth. For example, in 1991, bilateral negotiations led South Korea to begin defraying the cost of hosting U.S. troops. Both sides also are preparing a change in operational control in the event of war, moving from the existing structure of U.S. and South Korean soldiers operating under a binational command led by a U.S. general, to a binational command led by an ROK general with a U.S. deputy. Since 2022, the allies have upgraded their consultations over the U.S. extended deterrence commitment, partly to respond to growing calls within South Korea for the acquisition of an independent nuclear weapons capability. South Korea also has helped bolster trilateral security cooperation with the United States and Japan, particularly since a trilateral summit at Camp David in 2023.

The U.S.-ROK alliance may have reached an inflection point, some observers say, as the administrations of Donald Trump and Lee Jae Myung seek to further "modernize" the alliance. Amid rapidly changing threats by the People's Republic of China, Russia, and North Korea, Presidents Trump and Lee appear ready for South Korea to take a more active role in the alliance and to broaden the alliance's mission. President Lee has stated an intention for South Korea to acquire nuclear submarines, which President Trump says he supports. South Korea potentially could employ such submarines to counter North Korea and possibly China, though the wisdom of deploying ROK military assets against China is debated among ROK policymakers and experts. In addition, in November 2025, U.S. Secretary of Defense Pete Hegseth reporetedly stated that U.S. forces in South Korea could be used for a "regional contingency," which may include a China-Taiwan conflict.

Historically, Congress has supported the U.S.-ROK alliance on a broad, bipartisan basis. Through legislation, oversight, and other tools, Congress may direct and influence the executive branch's handling of the alliance. For instance, Members insert provisions related to South Korea and North Korea into the annual National Defense Authorization Act (NDAA). In addition, the House and Senate Armed Services Committees generally hold hearings the first quarter each year on U.S. military activities in the Indo-Pacific that include the commander of U.S. Forces Korea. During these hearings, Members may raise questions about U.S.-ROK joint war planning, the evolution of perceived regional threats, and other alliance issues.

As the U.S.-ROK alliance potentially enters a new period, Congress may face several key issues related to its legislative, oversight, and appropriations roles that could affect how the United States and South Korea navigate decisions, including:

• Should the United States alter its force presence in South Korea, and if so, how? What impact would increasing, reducing, or maintaining the U.S. force presence in South Korea have on U.S. national security interests, South Korea's security, and regional and global security?
• What might an alliance response look like in potential contingencies involving China, including around Taiwan or the South China Sea? What role, if any, would U.S. forces in South Korea potentially play in these scenarios?
• Should the United States promote U.S.-ROK-Japan cooperation, and if so, to what extent?
• In what ways do U.S.-ROK alliance planners incorporate the North Korean nuclear threat into policymaking, relative to other concerns such as China? Should the United States and South Korea adjust combined military exercises and other aspects of the alliance's posture to complement outreach to North Korea? If so, to what extent?
• Should Congress approve the Trump and Lee governments' plans for South Korea to acquire U.S. nuclear-powered submarine technology and U.S. approval to enrich and reprocess nuclear fuel?

---

The U.S.-South Korea Alliance and Congress's Role

The U.S.-South Korea (Republic of Korea; ROK) alliance dates back to the 1950-1953 Korean War, during which more than 36,000 Americans died in-theater helping South Korea repel a North Korean invasion.¹ In 1953, military commanders from the United States (representing the United Nations Command), the (North) Korean People's Army, and the Chinese People's Volunteer Army signed an Armistice Agreement. The United Nations General Assembly adopted the agreement the same year, and the Korean Peninsula remained divided at the 38^th Parallel (Figure 1). The combatants never signed a formal peace treaty, and the Korean Peninsula technically remains in a state of war.²

Figure 1. Map of the Korean Peninsula

Source: Created by CRS using Esri and based on data from the U.S. Department of State.

The United States and South Korea signed the U.S.-ROK Mutual Defense Treaty on October 1, 1953. The Senate provided its advice and consent to ratification of the Treaty on January 26, 1954, and President Eisenhower ratified it on February 5, 1954. The Treaty entered into force in November 1954.³ Under the Treaty, the United States and South Korea agreed "to defend themselves against external armed attack so that no potential aggressor could be under the illusion that either of them stands alone in the Pacific area."⁴ U.S. forces have maintained an ongoing presence on the Korean Peninsula under Article IV of the Treaty. The alliance traditionally has focused on the perceived North Korean threat, which has evolved as North Korea (formally known as the Democratic People's Republic of Korea, or DPRK) has developed its weapons of mass destruction (WMD) and missile capabilities.

As of February 2026, about 28,500 U.S. troops are stationed in South Korea, known as U.S. Forces Korea (USFK).⁵ USFK comprises predominately Army personnel operating some of the U.S. military's most advanced combat capabilities.⁶ Most U.S. troops in South Korea are assigned to Camp Humphreys, which underwent a major expansion in the 2010s and is the largest U.S. overseas military base in terms of land area.⁷ Meanwhile, overall ROK forces include about 570,000 active-duty servicemembers and another 3.1 million reservists.⁸ U.S. and South Korean forces face multiple risks from North Korea: North Korea continues to develop ballistic missiles and can strike the South Korean capital of Seoul with artillery fire.⁹ According to the Defense Intelligence Agency in its 2025 Worldwide Threat Assessment, the DPRK has a "nuclear-armed missile force operating ballistic and cruise missiles" that have the ability to reach U.S. forces in the Indo-Pacific.¹⁰ North Korea also is developing—and may have already developed—missiles with the capability to reach U.S. territory, including the U.S. homeland.¹¹

To prepare their forces to, if necessary, "fight tonight"—a USFK motto—the United States and South Korea have conducted combined and joint training and exercises, such as Freedom Shield (Figure 2). The exercises are designed to facilitate readiness and operational cohesion. North Korea has responded to drills, for example calling them "incursive, confrontational war rehearsal(s)."¹²

Successive U.S. presidential administrations generally have indicated strong support for the U.S.-South Korea alliance as a "linchpin" for security and stability on the Korean Peninsula and across the Indo-Pacific.¹³ Although U.S. alliance managers have particularly emphasized perceived threats by North Korea, they also have couched the role of the alliance in global terms, advancing cooperation in global health, cutting-edge technological development, and other areas. This cooperation is grounded in shared values and mutual trust.¹⁴

Figure 2. U.S. and South Korean Forces Conduct a Training Raid Associated with Bilateral Exercise Freedom Shield 25 March 19, 2025

Source: U.S. Forces Korea (USFK), https://www.usfk.mil/Media/Images/igphoto/2003671813/.

Congress historically has supported the U.S.-South Korea alliance on a broad, bipartisan basis. Through oversight, legislation, and other tools, Congress may routinely influence the executive branch's handling of the alliance. For example, the annual National Defense Authorization Act (NDAA) often contains provisions related to South Korea and North Korea. In addition, the House and Senate Armed Services Committees generally hold annual hearings in the first quarter of the year on U.S. military activities in the Indo-Pacific that include the Commander of U.S. Forces Korea. These hearings provide opportunities for Members to raise questions about U.S.-ROK joint war planning, the U.S. and ROK militaries' state of readiness, the evolution of perceived regional threats, the effectiveness of bilateral extended deterrence discussions, and other alliance issues.

In April 2023, then-South Korean President Yoon Suk-yeol addressed a Joint Meeting of Congress during his visit to Washington, DC, to mark the 70^th anniversary of the U.S.-ROK alliance. Yoon was the seventh South Korean president to give such an address and the first to do so since 2013.¹⁵ In his remarks, Yoon said the alliance has evolved into a "global alliance" that extends beyond traditional security, into artificial intelligence, quantum technology, outer space, and cyberspace.¹⁶

Support for maintaining and modernizing the alliance is broadly bipartisan, but U.S. policymakers, including in Congress, continue to debate how the allies should share the cost of maintaining U.S. forces in South Korea, the appropriate size of the U.S. troop presence, the role of USFK off the peninsula, and how the allies should share operational leadership.

Debates on these issues arise at a time when President Trump and ROK President Lee—both of whom took office in 2025—have expressed interest in changes to the alliance. President Trump's 2025 National Security Strategy (NSS) appears to reposition South Korea as a potential player not only in areas surrounding the Korean Peninsula, but also in broader U.S. regional security priorities. The NSS calls on allies including South Korea to develop the military capabilities "necessary to deter adversaries and protect the First Island Chain."¹⁷ Meanwhile, the latest National Defense Strategy says, "South Korea is capable of taking primary responsibility for deterring North Korea with critical but more limited U.S. support."¹⁸ Potentially as part of its goal to have South Korea lead more in the alliance, the Trump Administration has expressed support for South Korea's interest in acquiring nuclear submarines. Depending on the parameters of cooperation between the United States and South Korea on the development of nuclear-powered submarines, it could require a new bilateral nuclear cooperation agreement under the Atomic Energy Act (AEA) of 1954, as amended (P.L. 83-703; 42 U.S.C. §§2111 et seq).¹⁹ The Trump Administration also has indicated an increased focus on wider regional threats in the Indo-Pacific such as China, which could lead to the reconfiguration of U.S. forces in South Korea.²⁰ The Lee administration has pledged to increase ROK defense spending, purchase more U.S. weapons, and continue to modernize ROK forces.²¹ Both sides also have committed to accelerate changes to alliance command-and-control structures and enhance trilateral cooperation with Japan, topics touched on in the FY2026 NDAA.²²

Military Forces in South Korea

Three U.S.-led military commands on the Korean Peninsula support the ROK:

• U.S. Forces Korea (USFK, a unilateral U.S. command);
• United Nations Command (UNC, a multinational command led by the United States); and
• Combined Forces Command (CFC, a bilateral U.S./ROK command)

Through tradition and U.S.-ROK bilateral agreement, the USFK commander concurrently serves as commander of the UNC and CFC. If hostilities resumed on the Korean Peninsula, the CFC may lead U.S., South Korean, and multinational troops under the UNC.²⁷ As of February 2026, the three commands are led by U.S. Army General Xavier Brunson, whom the Senate confirmed for this role in September 2024.²⁸

(For a brief summary of the three U.S.-led commands—known as the "Tri-command"—see Table 1 below. For a map of USFK, UNC, and CFC bases, see Figure 3.)

U.S. Forces Korea (USFK)

Headquartered at Camp Humphreys, U.S. Forces Korea is a four-star level subordinate unified command, responsible for organizing, training, and equipping U.S. forces on the Korean Peninsula.²⁹ In his role as Commander of USFK, General Brunson reports to the commander of Indo-Pacific Command (USINDOPACOM), who in turn reports to the Secretary of Defense.³⁰

Components of USFK include but are not limited to:

• the Eighth Army, which provides the U.S. ground component on the Korean Peninsula;³¹
• the Seventh Air Force, responsible for the application of air power on the Korean Peninsula;³² and
• U.S. Naval Forces Korea, which assists the U.S. Seventh Fleet (based in Japan) and the ROK Navy with plans, policies, and training; it is based at Fleet Activities Chinhae, the only U.S. Navy installation in South Korea.³³

United Nations Command (UNC)

UN Security Council Resolutions 83 and 84 established the UNC in July 1950 in response to the outbreak of the Korean War, which began when North Korea invaded South Korea on June 25, 1950.³⁴ Member states—led by a U.S. commander—committed to defending South Korea and fought during the Korean War. UNSC Resolution 84 authorized "the unified command at its discretion to use the United Nations flag in the course of operations against North Korean forces concurrently with the flags of the various nations participating."³⁵ In 1953, U.S. General Mark Clark signed the Armistice Agreement on behalf of the UNC.³⁶ After the war, the UNC maintained operational control of South Korea's military until the establishment of the Combined Forces Command in 1978.

Under Armistice conditions, the UNC's responsibilities include enforcing the Armistice Agreement, coordinating contributions among UNC member states (known as "Sending States"), and facilitating dialogue with North Korea. UNC's staff is roughly 100 personnel.³⁷ The UNC Military Armistice Commission monitors compliance with the Armistice Agreement via inspections at the De-Militarized Zone (DMZ) at the border of North and South Korea and investigates alleged violations of the Armistice Agreement.³⁸ In addition, UNC-Rear "supports the transit and operation of UNC sending states' forces through Japan during the Armistice at designated UNC facilities. There are seven bases currently designated as UNC facilities in Japan, which fly the UN flag." These bases are shared with U.S. Forces Japan (USFJ).³⁹

If hostilities resume, the UNC—which has 18 member states—may provide "an efficient, exercised, and enduring platform to coordinate Sending State contributions to enable "security and stability on the Korean Peninsula."⁴⁰ The seven designated UNC-Rear bases across Japan may serve as logistic and supply bases to manage the flow of international forces into South Korea, aided by U.S. Forces Japan.⁴¹

Combined Forces Command (CFC)

The Combined Forces Command is a bilateral U.S./ROK headquarters established in 1978 to deter conflict with North Korea and, if necessary, lead U.S., ROK, and United Nations Command forces to defend South Korea. The CFC has no day-to-day assigned forces; rather, the CFC has temporarily assigned forces from both countries under Armistice conditions for combined military exercises to ensure combat readiness.⁴² Should hostilities resume, the CFC may be the designated theater-level operational command for those forces. Senior U.S. and ROK civilian leaders may jointly authorize the activation of the CFC and assign troops under its command if hostilities escalate beyond a certain threshold.⁴³

The CFC takes its direction from a bilateral steering committee called the Military Committee, which serves as a structure for high-level military coordination between the United States and South Korea. The Military Committee provides the CFC commander with bilaterally formulated guidance and direction. In addition, the U.S. Secretary of Defense (U.S. Secretary of War) and the ROK Minister of National Defense provide input or reaffirm decisions of the Military Committee via annual Security Consultative Meetings (SCMs).⁴⁴

Figure 3. Map of USFK, UNC, and CFC Bases

Source: CRS, using data from Esri. Notes: The Joint Security Area (JSA) is located at the Demilitarized Zone (DMZ); United Nations Command bases in Japan are co-located on U.S. Forces Japan (USFJ) facilities and referred to as "UNC-Rear."

South Korea's Defense Industry and Purchases of U.S. Weapon Systems

As of 2024, South Korea had the world's 11^th-largest military budget based on total monetary expenditures, spending roughly $47.6 billion or 2.6% of its gross domestic product (GDP).⁴⁵ South Korea has a mature and increasingly sophisticated defense industry and was the 8^th-largest defense exporter in 2023, measured as a share of the world's defense exports.⁴⁶ Internationally, South Korean firms compete in the aerospace, shipbuilding, and armored vehicles industries, among others.⁴⁷ One source's "Top 100" defense companies ranking for 2025 featured three South Korean defense companies—Hanwha, LIG Nex1, and Hyundai Rotem.⁴⁸ South Korea's latest program—Defense Innovation 4.0, announced in March 2023—aims to utilize advanced technologies such as artificial intelligence and unmanned systems to develop a more effective military less reliant on foreign sources of defense equipment. Defense Innovation 4.0 takes into account South Korea's low birth rate and declining population, which may impact future ROK troop strength.⁴⁹ President Lee has pledged to make South Korea the world's fourth-largest defense industry by increasing domestic production capacity and exports through 2030. His plan includes lowering barriers to entry for defense technology innovators and increased government investments in aerospace research and development.⁵⁰

South Korea is a major purchaser of U.S. defense articles and services through the Foreign Military Sales (FMS) and Direct Commercial Sales (DCS) programs. As of 2025, the United States has over $30 billion in active government-to-government sales cases with South Korea under the FMS System. Some recent FMS sales to South Korea that were notified to Congress include the F-35 Joint Strike Fighter, Patriot Advanced Capability-3 missile systems, Global Hawk Unmanned Aerial Vehicle, and Aegis Combat Systems. From FY2019 to FY2021, the United States authorized the export of over $3.4 billion in defense articles to South Korea via DCS, including gas turbine engines and military electronics.⁵¹ In November 2025, South Korea pledged to purchase $25 billion worth of U.S. military equipment by 2030.⁵²

The 110^th Congress passed legislation that upgraded South Korea's status as an arms purchaser from a "Major Non-NATO Ally" to the "NATO Plus Three" category (P.L. 110-429), which has subsequently become "NATO Plus Five." This upgrade increases the threshold for the requirement that the U.S. executive branch notify Congress of pending arms sales, from $14 million to $25 million. Congress has 15 days to consider the sale and take legislative steps to block the sale, compared to 30 days for Major Non-NATO Allies.

Key Issues for Congress

U.S. Troops Levels in South Korea

Since the U.S.-ROK Mutual Defense Treaty was signed in 1953, the United States gradually has reduced troop levels on the Korean Peninsula. These reductions often coincided with calls by some leaders in the United States for South Korea to contribute more to the alliance and/or with shifting U.S. global security priorities. President Eisenhower ordered the number decreased from around 75,000 to around 55,000 by 1960. In 1971, President Nixon withdrew the Seventh Infantry Division consisting of about 20,000 troops as part of the "Nixon Doctrine," which called for fewer U.S. troops in allied countries as those allies developed their own military power. President George W. Bush in 2004 ordered the withdrawal of 12,000 troops from South Korea, to be deployed to Iraq during the Iraq War. The number of U.S. troops has remained at around 28,500 since then (this number may include rotational troops).⁵³ (See Figure 4 for U.S. troop levels in South Korea over time.)

The issue of U.S. troop levels in South Korea continues to be a subject of debate amid changing political, security, and other dynamics, and it has become particularly relevant under President Trump. In his first term, President Trump reportedly planned to propose withdrawing all U.S. troops from South Korea, but advisors convinced him not to do so.⁵⁴ In the spring of 2025 during Trump's second term, the Trump Administration reportedly was considering relocating some 4,500 U.S. troops from South Korea to Guam and other locations in the Indo-Pacific region.⁵⁵ The Pentagon denied the report. Some experts say this idea stems from the Trump Administration's aim to reorient U.S. forces in the Indo-Pacific to focus on a potential conflict with China.⁵⁶

During a U.S.-ROK summit in Washington with President Lee on August 25, 2025, President Trump floated the idea of the United States taking ownership of land in South Korea where there are U.S. military facilities. While it has raised legal questions among some experts, it also may suggest that the Trump Administration intends to maintain a U.S. troop presence in South Korea.⁵⁷ In November 2025, U.S. Secretary of Defense Pete Hegseth and his ROK counterpart "reaffirmed that U.S. Forces Korea (USFK) will maintain force and posture levels to support Alliance efforts to prevent armed conflict on the Korean Peninsula and promote peace and stability in Northeast Asia."⁵⁸

Some experts have argued that the U.S. troop presence in South Korea is an integral part of the U.S. mutual defense commitment⁵⁹ and reducing the U.S. presence on the Korean Peninsula could raise questions among North and South Koreans about the credibility of that commitment.⁶⁰ Concerns about the U.S. commitment to South Korean security particularly might resonate if U.S. troops reductions come at a time when the Trump Administration's Department of Defense, which is "using a secondary Department of War designation," under Executive Order 14347 dated September 5, 2025, has already said it is prioritizing "reorienting toward deterring aggression by Communist China."⁶¹ Other analysts contend that South Korea is now capable of defending itself and that a continued U.S. presence is provocative to nuclear-armed North Korea, which may perceive the large U.S. military footprint as a threat.⁶² Rather than maintain a large force presence, they argue, the United States could instead seek to extract concessions from North Korea related to its nuclear program in exchange for reduced troop levels.⁶³

U.S. presidents generally have exercised wide latitude in altering the number of U.S. military personnel in South Korea, but Congress has taken an active role in shaping troop levels on the peninsula at times (for more, see the case studies on the Carter and first Trump Administrations below). Today, amid changing U.S./ROK assessments of the threats from the People's Republic of China (PRC, or China) and North Korea, the debate over U.S. troop numbers on the peninsula remains salient, as South Korea enhances its own military capabilities and President Trump has publicly expressed dissatisfaction with the asymmetric nature of the U.S.-ROK alliance.⁶⁴

Congress may wish to consider whether to support or oppose adjusting the number and composition of U.S. forces in South Korea. Congress also may consider the perceived strategic value of more U.S. forces in the INDOPACOM area of responsibility (AOR) to respond to a regional crisis, or the South Korean government's historical financial support for the U.S. troop presence there. Congress may also consider legislating in support of a smaller force presence in South Korea because the presence may be provocative to U.S. adversaries in the region, or based on uncertainty about South Korea's support for using U.S. forces based in South Korea for a conflict with China. Drawing upon its war-related powers, Congress could enact legislation that sets troop minimums or troop maximums.⁶⁵ In Section 1268 of the FY2026 NDAA (P.L. 119-60), Congress inserted a provision to prohibit the use of funds to reduce the approximate total number of U.S. troops permanently stationed in or deployed to South Korea below 28,500 until 60 days after the Secretary of Defense meets certain conditions. These conditions include certification by the Secretary to Congress that such a reduction serves U.S. national security interests and has been done in consultation with U.S. allies and partners, including South Korea and Japan. It would further require the Secretary to submit to the appropriate committees of Congress an analysis of the impact such a reduction may have on the security of the United States, South Korea, and Japan; U.S.-ROK joint activities and armed forces interoperability; and other considerations.

Members also may show support for or opposition to altering the U.S. troop presence in South Korea via open hearings, letters to the Administration, and/or other public statements. Congress may request briefings from the Department of Defense (also now Department of War) and other relevant executive agencies on the potential impact of an altered troop presence and related issues and commission committee reports to further investigate the topic.

Figure 4. U.S. Troops in South Korea, 1955-2023

Source: CRS, based on data from Dr. Tim Kane, "U.S. Troop Deployments, 1950-2023," American Lyceum, November 2024, https://www.ustroopdeployments.com/; U.S. Department of Defense.

"Strategic Flexibility": Alliance Coordination Off the Korean Peninsula

The U.S.-ROK alliance traditionally has focused on countering the DPRK threat. The level and make-up of U.S. forces in South Korea, as well as their training and exercise activities, are aimed at deterring and, if necessary, defeating North Korea. Over the decades, U.S. officials have wrestled with the question of whether, and to what extent, U.S. Forces Korea (USFK) should expand its activities to address broader regional threats, particularly with respect to Taiwan. In a January 2006 joint statement between then-U.S. Secretary of State Condoleezza Rice and then-ROK Foreign Minister Ban Ki-Moon, the countries "confirmed their understanding" that the ROK "respects the necessity for strategic flexibility of the U.S. forces in the ROK." The statement further provided:

The ROK, as an ally, fully understands the rationale for the transformation of the U.S. global military strategy…. In the implementation of strategic flexibility, the U.S. respects the ROK position that it shall not be involved in a regional conflict in Northeast Asia against the will of the Korean people.⁷¹

The allies issued this statement after the George W. Bush Administration announced it would redeploy roughly 3,600 U.S. troops from South Korea to Iraq as part of a policy to shift troops to where the United States deemed them most needed.⁷² The United States also announced it was reevaluating its force posture on the Korean Peninsula per the 2004 Global Defense Posture Review. These moves reportedly concerned South Korea. In addition, ROK officials increasingly feared that "strategic flexibility" of USFK could bring ROK forces into a conflict off the peninsula, particularly around Taiwan, which is discussed below.⁷³

As the nature of perceived threats has evolved, the United States and South Korea have sought to broaden the alliance's scope. In 2022, both sides agreed to upgrade the alliance to a "global comprehensive strategic alliance," meant to address not only North Korea but also larger cross-cutting issues such as cyber, economic, and health security.⁷⁴ The following year, U.S. and ROK military leaders agreed to a "Defense Vision of the U.S.-ROK Alliance" that includes promoting regional peace and stability bilaterally and with like-minded partners.⁷⁵

"Strategic flexibility" has received renewed attention as the second Trump Administration aims to modernize the U.S.-ROK alliance to more actively respond to threats not just from North Korea but also China. In U.S.-ROK joint statements in 2025—including at the Trump-Lee summit in November—both sides committed to "enhance U.S. conventional deterrence posture against all regional threats to the Alliance, including the DPRK."⁷⁶ At least one Member of Congress has expressed support for strategic flexibility of U.S. forces as long as (1) the U.S.-ROK alliance can continue to deter North Korea and (2) Congress plays an oversight role in discussions around strategic flexibility.⁷⁷

Role of U.S. Forces in a Potential Conflict over Taiwan

Some experts increasingly are discussing the role USFK may play in a possible conflict over Taiwan, the self-governing island democracy of 23 million people across the strait from mainland China, over which the PRC claims sovereignty. Publicly, senior U.S. military officials have cast the U.S.-ROK alliance's responsibilities in broad regional terms that suggest the alliance could have a role to play if conflict breaks out over Taiwan. USFK Commander General Xavier Brunson reportedly has said that USFK is "not solely focused on deterring North Korea but also part of a broader Indo-Pacific strategy."⁷⁸ In 2022, former USFK Commander Robert Abrams reportedly said the United States would keep "all options" open regarding which forces it might use in a conflict over Taiwan, including USFK.⁷⁹

The second Trump Administration describes China as the overseas "pacing threat" and appears to be repurposing USFK for potential use in a Taiwan contingency.⁸⁰ For example, the U.S. Air Force established a permanent presence of MQ-9 Reaper drones at Kunsan Air Base on South Korea's west coast in September 2025.⁸¹ The drones reportedly will support intelligence, surveillance, and reconnaissance operations, and their range covers the DMZ as well as the East China Sea and Taiwan.⁸² Some defense experts say that a dual-purpose USFK prepared for threats on the Korean Peninsula and in the Taiwan Strait aligns with U.S. theater-wide deterrence efforts—particularly vis-à-vis China—and argue its value would be greater if the United States deployed precision strike and other advanced military capabilities on the peninsula. However, if a conflict around Taiwan broke out, some experts have questioned whether redistributing troops may reduce readiness or increase South Korea's vulnerability to PRC or North Korean provocations.⁸³ In addition, USFK largely consists of U.S. Army ground forces, and in its configuration as of February 2026, USFK's effectiveness for use in a Taiwan conflict may be limited.⁸⁴ Some observers have noted that the Trump Administration could decide to bolster air and naval assets on the peninsula while reducing ground forces to better counter PRC and other regional threats.⁸⁵

Role of ROK Forces in a Potential Conflict over Taiwan

Even if USFK were to adopt a dual-purpose posture, it is less clear what role ROK forces might play in a conflict over Taiwan. South Korean civilian and military leadership have taken a more cautious approach to questions about possible ROK actions in the event of a cross-Strait conflict. This caution may find its roots in multiple South Korean concerns, including U.S. abandonment if USFK were deployed off the peninsula; entanglement of South Korean forces in a regional conflict; and the possibility that North Korea might seek to take advantage of a distracted United States during a Taiwan conflict and undertake military provocations against South Korea. Such scenarios may make U.S. and ROK bases in South Korea a target. South Korean officials have argued that in any conflict, the ROK military should remain focused on the North Korean threat.⁸⁶

In a Taiwan contingency, some analysts expect U.S. policymakers to count on South Korea to continue deterring North Korea and provide indirect military assistance to Taiwan, such as logistical support for U.S. forces and reconnaissance against PRC military assets.⁸⁷ In 2022, then-President Yoon underscored that in the event of a Taiwan contingency, "the top priority for … the U.S. Korean alliance on the Korean peninsula would be based on our robust defense posture, [so] we [South Korea] must deal with the North Korean threat first."⁸⁸ While campaigning, current President Lee was asked whether, if he were elected, South Korea would aid Taiwan if China attacked it. "I will think about that answer when aliens are about to invade the earth," Lee replied.⁸⁹ More broadly, if South Korea intends to pursue the development of nuclear-powered submarines, some U.S. officials have said the United States would expect South Korea to use those submarines to support combined efforts to counteract China in the region.⁹⁰

Congress, "Strategic Flexibility," and Taiwan

Whether South Korea would allow U.S. forces based on its territory to conduct offensive operations against China in a Taiwan contingency is a highly sensitive and unsettled issue. The U.S.-ROK Mutual Defense Treaty grants to the United States "the right to dispose United States land, air and sea forces in and about the territory of the Republic of Korea as determined by mutual agreement." The Department of Defense (DOD)'s ability to use these locations may be affected by political developments beyond U.S. control. South Korea might oppose the use of U.S. forces on the Korea Peninsula for a variety of reasons, including a South Korean reluctance to provoke China, or a preference to keep all U.S. forces in South Korea focused on the threat of North Korea, or a political leadership that feels a reluctance to support a U.S.-China contingency operation.

Congress may consider these uncertainties when making decisions about funding the U.S. force posture in South Korea, or when considering legislation that would affect the size and scope of the U.S. force posture in South Korea. Congress also may consider whether or not DOD adequately accounts for this kind of political risk in its strategic and operational planning. If Congress identifies concerns with DOD's approach, Congress could direct DOD to develop new plans, strategies, or reports to address these risks.

Cost Sharing

Since 1991, South Korea has offset the cost of stationing U.S. forces on the Korean Peninsula via so-called "Special Measures Agreements" (SMAs).⁹⁷ U.S.-ROK SMAs signed since the late-2000s generally have lasted five years. ROK payments—a combination of in-kind and cash contributions—fall into three categories: labor (salaries for South Koreans who work on U.S. bases); logistics; and construction (by ROK firms for U.S. facilities). A 2021 analysis from the Government Accountability Office (GAO) found that South Korea provided $3.3 billion cumulatively in both cash and in-kind financial support from 2016 through 2019.⁹⁸

American domestic fiscal concerns largely prompted the first SMA in 1991.⁹⁹ In the late 1980s, the United States experienced growing budget deficits, prompting calls for South Korea to pay more to support U.S. Forces Korea (USFK), particularly since South Korea had emerged as a middle-income country. These calls coincided with a gradual reduction of U.S. troop levels on the Korean Peninsula. Some Members of Congress asserted that South Korea should offset more of the direct costs incurred by USFK and take more responsibility for its own security (for example, see S. 1439 in the 101^st Congress (1989-1990)).

U.S.-ROK SMAs contain "special measures"—or exceptions—related to Article V of the Status of Forces Agreement (SOFA), which entered into force in 1967 and provides a legal framework for how U.S. military personnel operate in South Korea. Article V stipulates that the United States will cover all costs for maintaining its military presence in the ROK, with the exception of costs associated with facilities.¹⁰⁰ (The SOFA was concluded pursuant to Article IV of the U.S.-ROK Mutual Defense Treaty, which states that the ROK grants to the United States "the right to dispose United States land, air and sea forces in and about the territory of the Republic of Korea as determined by mutual agreement.")

Although U.S.-ROK burden-sharing talks historically have been contentious, they became particularly divisive during the first Trump Administration due to U.S. requests for steep increases in ROK contributions.¹⁰¹ President Trump reportedly asked South Korea to increase its contribution by roughly 400%.¹⁰² Amid an impasse, the two countries signed a one-year stop-gap SMA covering the 2019 calendar year that raised South Korea's annual contribution by around 8%.¹⁰³ After the two sides were unable to bridge their differences in subsequent negotiations over a longer-term SMA, about 4,500 South Koreans who worked on U.S. bases were furloughed after the 2019 stop-gap SMA expired in December 2019. The two sides were unable to reach an agreement in 2020. At the time, some Members of Congress expressed concerns about the lapse, warning of potential negative impacts on U.S. military operations and readiness in the Indo-Pacific region.¹⁰⁴ Then-USFK Commander Gen. Robert Abrams also voiced concerns.¹⁰⁵ In March 2021, the Biden Administration concluded a new five-year SMA. Under that 11^th SMA, South Korea agreed to pay about $1 billion in 2021, a 13.9% increase from the 2019 SMA. Subsequent annual increases were tied to increases in South Korea's defense budget. The agreement entered into force in 2021 and applied retroactively to all of calendar year 2020.¹⁰⁶

On November 4, 2024, the United States and South Korea concluded the 12^th SMA. According to the Biden Administration upon finalizing the text, the deal would "strengthen our Alliance and our shared defense."¹⁰⁷ The SMA entered into force on November 29, a day after ratification by the ROK National Assembly.¹⁰⁸ This 12^th SMA covers the years 2026-2030 and increases South Korea's 2025 contribution by 8.3%, to roughly $1.19 billion in 2026.¹⁰⁹ Under the SMA, subsequent annual increases are tied to South Korea's inflation rate and "shall not exceed" 5%.¹¹⁰ Like its immediate predecessor, the 12^th SMA includes a mechanism for South Korean workers on U.S. bases to be paid for up to a year after the agreement expires, upon the request of the United States. The mechanism is designed to minimize the risk of South Korean base workers being furloughed as they were in 2020.

In a break from previous patterns, the two allies concluded the 12^th SMA more than a year before the 11^th SMA was set to expire in December 2025.¹¹¹ The Biden Administration concluded the 12^th SMA with South Korea as an executive agreement, and—as was the case with its predecessor agreements—the President did not submit it to Congress for approval. Some observers speculated the Biden Administration and South Korea negotiated the 12^th SMA earlier than usual to insulate the U.S.-ROK alliance from possible policy shifts if President Trump were reelected to office.¹¹²

In November 2025, Presidents Trump and Lee announced that South Korea had "shared its plan to provide comprehensive support for U.S. Forces Korea amounting to $33 billion in accordance with ROK legal requirements."¹¹³ It is unclear how this plan interacts with or relates to the 12^th SMA, but ROK National Security Advisor Wi Sung-lac reportedly has said the $33 billion figure could include indirect costs such as waived taxes and fees for U.S. troops in South Korea.¹¹⁴ Such indirect costs typically have not been part of SMAs.¹¹⁵

Congress may choose to utilize various tools to influence U.S.-ROK cost-sharing negotiations and agreements. Initially, Congress could use its oversight authority to conduct hearings on the executive branch's implementation of the SMA or to establish congressional notification and reporting requirements. Congress may consider whether to exercise its spending power to encourage the executive branch to pursue Congress's preferred posture toward the SMA. Congress also could increase or decrease funding for the bilateral alliance to advance its policy toward the 12^th SMA. Congress also may choose to seek clarification as to how the reported $33 billion in ROK contributions to USFK factor into the 12^th SMA, and what understanding the United States and South Korea have regarding the timeframe for the contributions, specific areas of support for USFK, and other details.

Chain of Command/Wartime Operational Control

For nearly three decades, U.S. and ROK leaders have discussed changing the way U.S. and ROK forces are integrated. In particular, the two allies are in the process of changing operational control, or OPCON, a military term that refers to the legal authority to direct and control military forces in the execution of missions or wartime operations. Under the current arrangement, each country retains operational control of its forces under armistice conditions (conditions short of war).¹¹⁶ In the event that hostilities on the Korean Peninsula escalate beyond a certain threshold, the United States and South Korea may decide to activate the Combined Forces Command (CFC) and implement a "wartime OPCON" structure for directing military forces. Under the current arrangement, this structure would put U.S. and ROK forces under the CFC's command, led by a four-star U.S. general with a South Korean deputy.¹¹⁷ Neither country would relinquish command authority over its own troops.

In 2007, the U.S. and ROK reached a bilateral agreement to change the wartime OPCON structure, but it remains unimplemented (see below). Under the wartime OPCON structure laid out in the 2007 agreement, an ROK general would become the CFC head, and the U.S. general would serve as deputy. As is the case under the current (pre-OPCON transfer) arrangement, neither country would relinquish command authority over its own troops.¹¹⁸ The 2007 agreement to change wartime OPCON, which President George W. Bush reached with progressive ROK President Roh Moo-hyun (in office 2003-2008), was intended to reflect the ROK's advances in economic and military strength and place the military allies on more equal footing.

Congress may consider whether or not to conduct oversight of this issue. In the FY2024 NDAA (P.L. 118-31), Congress required the Secretary of Defense and Secretary of State to submit a report to Congress describing under what conditions South Korean military forces would be ready to assume wartime operational control of the CFC, and to what extent the South Korean military meets such conditions. In Section 1268 of the FY2026 NDAA (P.L. 119-60), Congress inserted a provision to prohibit the use of funds to complete the transition of wartime OPCON "in a manner which deviates from a bilaterally agreed plan to effectuate such a transition" until 60 days after the Secretary of Defense meets certain conditions. These conditions include a certification to Congress that the transition "is in the national security interest of the United States" and includes consultations with U.S. allies and partners, including South Korea and Japan. In addition, the Secretary would be required to submit an assessment to Congress that includes how the ROK-led CFC would report to U.S. and ROK national command authorities, and other details. Members may opt to include or omit such provisions in future legislation.

Congress also may consider holding public or classified hearings on the state of U.S.-ROK combined readiness as well as U.S. military officials' assessments of present and future ROK military capabilities that could lead to the transfer of wartime OPCON.

Delays and Reassessment of OPCON Transition Plan

The United States and South Korea have twice delayed implementation of the wartime OPCON plan, both times under conservative South Korean presidents. In 2010, when Lee Myung-bak was president (in office 2008-2013), the implementation was postponed to 2015 after North Korea's second nuclear test in 2009 and the sinking of South Korean Navy vessel Cheonan in 2010 raised concerns over whether South Korean forces were adequately prepared to assume OPCON responsibility.

As the 2015 deadline approached, South Korean officials under President Park Geun-hye (in office 2013-2017) reportedly worried that their military was not fully prepared for North Korean threats and that Pyongyang might interpret implementation of the wartime OPCON plan as a weakening of the alliance's deterrence.¹¹⁹ In October 2014, the United States and South Korea announced they would take a "conditions-based approach" to the wartime OPCON plan.¹²⁰ The most recent version of the plan is the 2018 Conditions-based Wartime Operational Control (OPCON) Transition Plan (COTP) Change One.¹²¹ This plan lays out three bilaterally agreed-upon benchmarks that must be fulfilled before the transfer can take place. These benchmarks assess three conditions:

• 1. "Military capabilities of South Korean forces required to lead the combined defense;
• 2. "Comprehensive Alliance response capabilities against North Korean nuclear and missile threats; and
• 3. "Security environment on the Korean peninsula and in the region that is conducive to a stable transition of the wartime OPCON."¹²²

Both sides continue to monitor capabilities and readiness regarding Conditions 1 and 2. In meeting Condition 3, U.S. and South Korean defense officials have said they would "remain in close consultation for the assessment of the security environment."¹²³

Debate Around OPCON Plan Implementation

Wartime OPCON plan implementation has generated debate in South Korea. Generally, progressive South Korean leaders (such as former President Moon Jae-in, who was in office from 2017-2022) have favored greater national autonomy within the alliance. Some South Korean progressives have argued implementation is necessary for their country to achieve complete control over national sovereignty and self-defense.¹²⁴ Conservative South Korean leaders (such as former President Yoon Suk-yeol, who was in office from 2022 to 2025) have tended to be more comfortable with the status quo. The administration of President Lee Jae Myung, a progressive, reportedly has proposed to achieve the OPCON transfer by 2030."¹²⁵ In November 2025, the United States and South Korea agreed to "develop a roadmap to acquire the capabilities necessary to expedite the fulfillment of conditions required for wartime OPCON transition" and move forward with the second of a three-phase assessment of ROK capabilities in 2026.¹²⁶

Some experts note that the CFC commander reports directly to the U.S. and South Korean presidents, who in turn decide whether to provide troops to the CFC from their respective militaries. The nationality of the CFC commander is largely immaterial, they say, and therefore the issue is not related to ROK sovereignty.¹²⁷ Other defense analysts have cautioned that the implementation of the 2007 OPCON agreement could diminish the CFC's role and reduce the extent of U.S. involvement in a potential security contingency on the peninsula.¹²⁸

OPCON and the United Nations Command

Transitioning wartime OPCON control to the South Korean military also has raised questions about the future role of the United Nations Command (UNC). Under the current arrangement, a U.S. four-star general leads the CFC, UNC, and USFK, making him "triple-hatted." After the transition, the USFK commander would continue to lead the UNC. Some experts say that a South Korean commander heading the CFC may pose challenges for CFC-UNC-USFK defense coordination. As a result, they argue, the alliance should ensure smooth coordination among the three commands, and particularly between the South Korean-led CFC and the UNC, which has bases across South Korea and Japan.¹²⁹ The UNC-Rear bases in Japan would be critical hubs to facilitate the flow of non-U.S./non-ROK international forces in a conflict.

Extended Deterrence on the Korean Peninsula and South Korea's Nuclear Armament Debate¹³⁰

The U.S.-ROK Mutual Defense Treaty provides extended deterrence—the ability and commitment of the United States to deter attack against South Korea, including nuclear attack. Extended deterrence may include a U.S. nuclear response and is sometimes referred to as the "nuclear umbrella." ROK concerns around extended deterrence largely stem from U.S. ambiguity in official statements—that is, the United States has neither publicly nor explicitly committed to a nuclear, rather than conventional, response against North Korea in a conflict if North Korea (officially the Democratic People's Republic of Korea, or DPRK) used nuclear weapons against South Korea. The U.S. 2022 Nuclear Posture Review (NPR) states, "Any nuclear attack by North Korea against the United States or its Allies and partners is unacceptable and will result in the end of that regime."¹³¹ The NPR also states that "as long as Allies and partners face nuclear threats, extended nuclear deterrence will remain a pillar of regional security architectures."¹³² The NPR says this system is based on "ally and partner confidence that the United States has the will and capability to meet its security commitments." The United States extends nuclear deterrence to its allies through missile defenses, forward-deployed nuclear weapons, and U.S.-based aircraft capable of conventional or nuclear missions that could be deployed in a crisis. Extended deterrence also includes consultations, joint exercises and planning, and U.S. force presence.¹³³

Since the early 2000s, multiple North Korean nuclear weapon and missile tests have sharpened North Korea's threat to South Korea. Advancing DPRK capabilities, including its potential ability to reach the continental United States with inter-continental ballistic missiles (ICBMs), have increased uncertainty in the ROK about the credibility of U.S. security guarantees and heightened a sense of vulnerability to North Korean threats.¹³⁴ In response to South Korean concerns, in July 2016, the U.S. and South Korean governments agreed to deploy a Terminal High Altitude Area Defense (THAAD) battery to U.S. Forces Korea. The THAAD battery is stationed at a South Korean military base in Seongju, about 130 miles south of Seoul.¹³⁵ A Department of Defense (also now Department of War) press release said the deployment's purpose was to "ensure the security of South Korea and that of its people, and to protect alliance military forces from North Korea's weapons of mass destruction and ballistic missile threats."¹³⁶ The system undergoes periodic updates to respond to North Korean threats.¹³⁷

Over the past decade, some South Koreans have advocated for the U.S. redeployment of tactical nuclear weapons to the country; the United States withdrew nuclear weapons from the Korean Peninsula in 1991.¹³⁸ Others have argued for South Korea to develop its own nuclear weapons. Some public opinion polls in the last 10 years also suggest a majority of the South Korean public supports developing a domestic nuclear weapons capability and has confidence in U.S. alliance commitments.¹³⁹ Strategic thinkers in South Korea, such as academics, business leaders, and government officials, generally appear less enthusiastic about an independent nuclear deterrent.¹⁴⁰ Conservative South Korean politicians have tended to favor ROK nuclear armament more than their progressive counterparts, with North Korea as the primary motivator. President Lee Jae Myung has said he opposes both redeployment of U.S. tactical nuclear weapons and South Korea developing its own nuclear weapons because doing so could lead to strong pushback from the international community.¹⁴¹ At a December 3, 2025, press conference, President Lee said, "The denuclearization of the Korean Peninsula is a fundamental principle agreed upon by both North and South, and we have no intention of deviating from it."¹⁴²

Figure 5. Ohio-Class Ballistic-Missile Submarine USS Kentucky Enters Busan, South Korea, for a Port Visit in July 2023

Source: U.S. Strategic Command.

In an apparent bid to reassure South Koreans skeptical of U.S. extended deterrence—and discourage South Korean nuclear ambitions—the two governments issued the "Washington Declaration" during then-President Yoon's 2023 State Visit to the White House.¹⁴³ Presidents Biden and Yoon announced new efforts to increase nuclear deterrence consultations, reaffirmed Washington's pledge to Seoul, and clarified Seoul's nonproliferation commitments. The Washington Declaration states that the ROK has "full confidence in U.S. extended deterrence commitments and recognizes the importance, necessity, and benefit of its enduring reliance on the U.S. nuclear deterrent."¹⁴⁴ It also reaffirms South Korea's commitment to the Nuclear Nonproliferation Treaty (NPT), under which it commits to not developing nuclear weapons.

The Washington Declaration articulated a pledge to enhance bilateral planning, exercises, and other consultations related to nuclear deterrence. It established a Nuclear Consultative Group (NCG), which met for the first time in June 2023.¹⁴⁵ The NCG is intended to align and advance efforts to bolster deterrence against DPRK nuclear threats, with a particular emphasis on joint planning for ROK conventional support to U.S. nuclear operations and on enhancing the visibility of U.S. "strategic asset deployments" to the peninsula.¹⁴⁶ To demonstrate the U.S. commitment to extended deterrence after the Washington Declaration, the Biden Administration sent the nuclear-capable ballistic-missile submarine USS Kentucky to Busan in July 2023, the first visit by a U.S. ballistic-missile submarine to South Korea in decades (Figure 5).¹⁴⁷

The United States continues to offer statements of reassurance about the alliance. A bilateral joint statement at the Fourth Nuclear Consultative Group meeting on January 10, 2025, said, "any nuclear attack by the DPRK against the United States or its allies is unacceptable and will result in the end of that regime. The U.S. commitment to extended deterrence to the ROK is backed by the full range of U.S. capabilities, including nuclear."¹⁴⁸ U.S. officials repeated that commitment after a bilateral meeting of top defense and foreign affairs officials on November 3-4, 2025.¹⁴⁹ In December 2025, the NCG held its first meeting under the second Trump Administration.

Congress's Role in Extended Deterrence

The Senate provided its advice and consent to ratification of the U.S.-ROK Mutual Defense Treaty on January 26, 1954.¹⁵⁰ On the occasion of the Treaty's 70^th anniversary in 2024, the House and Senate introduced bills commemorating the Treaty and recognizing the importance of the alliance.¹⁵¹ The Senate-passed resolution (S.Res. 175) says, "the United States assures its ironclad security commitment to the Republic of Korea, including the United States extended deterrent underpinned by the full range of United States capabilities, including nuclear capabilities." In addition to standalone bills, Congress has expressed support for the alliance as part of the defense authorization process. For example, Section 1344 of the FY2025 National Defense Authorization Act (P.L. 118-159) required the Secretary of Defense (also now Secretary of War) to submit a plan to Congress by March 1, 2025, to include a description of "resources, budget, and personnel needed to strengthen United States extended deterrence commitments to the Republic of Korea," including nuclear consultations, strategic planning and related activities. Section 1271 of the FY2026 NDAA (P.L. 119-60) prohibits the use of certain funds defense-wide and available for the Office of the Secretary of Defense until the Secretary of Defense submits the aforementioned report to Congress. Congress also reviews these policies through hearings such as the annual Indo-Pacific military posture hearings in the armed services committees.¹⁵²

U.S.-ROK-Japan Trilateral Cooperation

Figure 6. ROK President Yoon, U.S. President Biden, and Japanese Prime Minister Kishida at Camp David August 18, 2023

Source: The White House 46 Archived, on X.

U.S.-ROK-Japan trilateral coordination reached unprecedented levels under Presidents Biden and Yoon, and then-Japanese Prime Minister Kishida, at the August 2023 Camp David Summit (Figure 6). The three leaders—who are all now out of office—announced several initiatives for a "new era of trilateral partnership" that included pledges to convene trilateral meetings at high levels (including an annual leaders' meeting), expand trilateral military exercises, and abide by a "Commitment to Consult" on regional conflicts and challenges. South Korea-Japan relations historically have been fraught because of a territorial dispute and sensitive issues stemming from Japan's colonization of the Korean Peninsula from 1910 to 1945. Beginning in 2018, a series of actions and retaliatory countermeasures by both governments involving trade, security, and history-related controversies caused South Korea-Japan relations to plummet, eroding U.S.-ROK-Japan policy coordination.

For over a decade, Members of Congress have expressed support for deeper U.S.-ROK-Japan cooperation and concern when relations between Seoul and Tokyo have taken a downturn.¹⁵³ A cooperative relationship between the two countries and among the three benefits U.S. interests because it arguably enhances regional stability, helps coordination over North Korea policy, and boosts each country's ability to deal with the strategic challenges posed by China's rise.

Congress may choose to issue joint resolutions expressing support for and reaffirming the importance of trilateral cooperation. It also may consider whether or not to mandate the Department of Defense and Department of State to report on progress over multiple years on the development of the trilateral secretariat established in 2024, multidomain military exercises, information sharing, and other areas of security and diplomatic engagement. Section 1271 of the FY2026 NDAA (P.L. 119-60) prohibits the use of certain funds defense-wide and available for the Office of the Secretary of Defense until the Secretary of Defense submits to Congress a report on how he intends to advanced U.S.-ROK-Japan trilateral cooperation, as required by the FY2025 NDAA (P.L. 118-159). Members may choose to hold hearings with senior U.S. defense officials and experts assessing the current state of trilateral cooperation, contextualized by U.S. strategic objectives regionally and globally. In addition, Congress may opt to continue, stop, increase, or decrease funding U.S. contributions to trilateral cooperation-related activities, such as the military exercises and other efforts.

U.S.-South Korean Cooperation on Shipbuilding¹⁵⁴

Delays in U.S. Navy shipbuilding programs, U.S. shipbuilding capacity constraints, and maintenance backlogs for Navy ships—particularly when viewed in comparison to China's naval and commercial shipbuilding activities and China's much-larger shipbuilding capacity—have prompted discussions in Congress about options for accelerating the construction of new Navy ships, reducing Navy ship maintenance backlogs, and increasing the capacity of the U.S. shipbuilding industry.¹⁵⁵ (For more on U.S. shipbuilding capacity, see CRS Report RL32665, Navy Force Structure and Shipbuilding Plans: Background and Issues for Congress, by Ronald O'Rourke.) Within these discussions, some observers have focused on options for increasing U.S. cooperation on shipbuilding with South Korea and Japan, whose shipbuilders are widely regarded as being among the world's most modern and efficient. Potential areas of U.S. cooperation with South Korea on shipbuilding include the following:

• sharing of shipbuilding best practices;
• investment by South Korean shipbuilders in U.S. shipyards;
• conducting maintenance, repair, and overhaul (MRO) work on U.S. Navy ships in South Korean shipyards; and
• building new ships for the U.S. Navy in South Korean shipyards.

The United States and South Korea cooperate in the first three areas above. As an example of cooperation in the first area, in April 2025, the U.S. shipbuilder Huntington Ingalls Industries (one of the top builders of new ships for the U.S. Navy) signed a memorandum of understanding (MOU) with Hyundai Heavy Industries (one of South Korea's top three shipbuilders) for the sharing of shipbuilding best practices.¹⁵⁶ Regarding the second area listed above, in August 2025, the South Korean government pledged to invest $150 billion to support shipbuilding in the United States as part of a broader bilateral trade deal. The investment project—called "Make American Shipbuilding Great Again," or MASGA—reportedly would enable South Korean shipbuilders to create new shipyards in the United States and reestablish shipbuilding supply chains.¹⁵⁷ The details and timeline for investments remain unclear, but the $150 billion may largely consist of loan guarantees rather than direct investments.¹⁵⁸ In addition, in December 2024, Hanwha (another one of South Korea's top three shipbuilders) completed its purchase of Philly Shipyard in Philadelphia, a builder of ships for the U.S. government that had been owned by the Norwegian firm Aker ASA. Hanwha plans to modernize and expand operations at the shipyard, which is now known as Hanwha Philly Shipyard, and in August 2025 Hanwha committed $5 billion as part of the $150 MAGSA project.¹⁵⁹ Regarding the third area above, South Korean shipyards have performed MRO work on certain U.S. military ships.¹⁶⁰ The fourth area listed above—building new ships for the U.S. Navy in South Korean shipyards—has not occurred.

Two issues for Congress are whether cooperation in one or more of the first three areas could or should be increased, and whether to initiate cooperation in the fourth area. Congress may consider whether or not to publicly encourage bilateral cooperation in the first three areas and could hold hearings on the impacts of such cooperation on U.S. economic security interests. South Korean shipyards have expressed interest in continuing to conduct MRO work on U.S. military ships, and in building ships for the U.S. Navy.¹⁶¹ Some other observers have similarly suggested using South Korean (or Japanese) shipyards to build ships for the U.S. Navy as a near-term or stop-gap means of responding to U.S. shipbuilding capacity constraints.¹⁶² In April 2025, President Trump reportedly expressed openness to the idea of purchasing foreign-built ships for the Navy.¹⁶³ The potential for expanded U.S.-South Korean cooperation in shipbuilding has gained prominence in overall U.S.-South Korean relations.¹⁶⁴

The ability of foreign shipyards to perform MRO work on U.S. military ships is limited by 10 U.S.C. §8680. The building of ships in foreign shipyards for U.S. armed forces is prohibited by 10 U.S.C. §8679 and (for U.S. Coast Guard ships) by 14 U.S.C. §1151. Both of these statutes permit presidential waivers and exceptions for the national security interest, with the President required to submit a notification to Congress 30 days prior to making a contract pursuant to an exception or waiver. The building of ships for the Navy is additionally prohibited by a recurring provision in the annual Department of Defense appropriations act that has not included a presidential waiver or exception. Supporters in Congress and elsewhere of 10 U.S.C. §8680, 10 U.S.C. §8679, 14 U.S.C. §1151, and the recurring provision in the annual DOD appropriations act argue that these provisions help preserve U.S. shipbuilding capacity and U.S. shipbuilding jobs, and that expanding the use of foreign shipyards for performing MRO work on U.S. military ships or using foreign shipyards to build new ships for the Navy could be detrimental to U.S. shipbuilding capacity and expose the United States to foreign supply chains that could be vulnerable in wartime.¹⁶⁵ Congress may choose to amend (or even repeal) 10 U.S.C. §8679 and 14 U.S.C. §1151 in a number of ways. For example, S. 406 (Ensuring Naval Readiness Act) and S. 407 (Ensuring Coast Guard Readiness Act) would allow the President to issue waivers if the foreign shipyard is "located in a North Atlantic Treaty Organization member country or a country in the Indo-Pacific region that is party to a mutual defense treaty with the United States." Both bills would further require the Secretary of the Navy and Commandant of the Coast Guard, respectively, to certify to Congress that the foreign shipyard is not "owned or operated by a Chinese company or a multinational company domiciled in the People's Republic of China." In addition, Congress may request briefings from U.S. national security officials on the potential merits and risks of constructing U.S. Navy and Coast Guard vessels in foreign shipyards.

U.S.-ROK Alignment on North Korea

Figure 7. President Trump and Kim Jong-Un at Hanoi Summit February 2019

Source: Trump White House Archived on Flickr.

Since the breakdown of nuclear diplomacy between President Trump and North Korean leader Kim Jong-un in Hanoi in 2019, the United States and North Korea have had little substantive contact (Figure 7). During that time, North Korea has advanced key aspects of its military forces, including its strategic weapons.¹⁶⁶ President Trump has expressed interest in meeting with Kim "in the appropriate future."¹⁶⁷ Some observers say South Korea fears it could be excluded from such talks.¹⁶⁸ South Korean President Lee Jae Myung has said he will "keep channels of communication with North Korea open and pursue peace on the Korean Peninsula through dialogue and cooperation."¹⁶⁹

The second Trump Administration and Lee administration appear to diverge over whether to modify U.S.-ROK combined military exercises to create space for dialogue with North Korea. U.S. officials have cited the importance of bilateral exercises for maintaining military readiness, while some ROK officials have suggested that scaling them back could ease tension with North Korea and create opportunity for dialogue.¹⁷⁰

To enhance U.S.-ROK security alignment on North Korea, Congress could consider how the alliance's strategic framing incorporates North Korea relative to other regional concerns, such as China. Congress could request briefings from the Department of Defense or other executive branch agencies to learn more on current thinking and future plans for the U.S.-ROK alliance. In tandem with briefings, Congress could mandate annual reports across several years on how the Administration and its South Korean counterpart are planning for contingencies involving North Korea and what concrete steps the two allies are taking to further deter Kim from aggression and return to denuclearization negotiations.

On the other hand, if Congress were to seek to support a more unilateral approach to North Korea, it could require executive branch reports on how the administration plans to engage with the Kim regime outside the U.S.-ROK alliance and what impacts such engagement are likely to have on regional security dynamics.

Appendix A. Legislation Related to U.S.-South Korea Security Issues from the 118^th Congress

P.L. 118-159, Servicemember Quality of Life Improvement and National Defense Authorization Act for Fiscal Year 2025. Section 1311 expressed the sense of Congress that the United States should reinforce its alliance with South Korea, including by maintaining the current force posture of 28,500 servicemembers on the Korean Peninsula and strengthening "mutual defense base cooperation." Section 1344 required the Department of Defense no later than March 1, 2025, to submit to Congress a plan to "strengthen United States extended deterrence commitments to the Republic of Korea as identified in the December 16, 2023, Joint Press Statement on the United States-Republic of Korea Nuclear Consultative Group." Section 1345 required the Secretary of Defense to submit to Congress by March 1, 2025, a plan "to advance trilateral defense cooperation among the United States, Japan, and the Republic of Korea." The report was to have covered trilateral communication mechanisms, ballistic missile defense, trilateral military exercises, and countering malicious cyber activities. H.R. 5009 was passed by the House on 12/11/2024 (281-140, Roll no. 500); it was passed by the Senate on 12/18/2024 (85-14, Record Vote Number: 325); it was signed by the President on 12/23/2024.

P.L. 118-31, the National Defense Authorization Act for Fiscal Year 2024. Section 1301 expressed the sense of Congress that the United States should reinforce its alliance with South Korea, including by maintaining the 28,500 U.S. troops stationed in South Korea and by enhancing bilateral coordination on extended deterrence as noted in the Washington Declaration adopted on April 26, 2023. Section 1318 required the Secretary of Defense and Secretary of State to submit a report to Congress describing under what conditions South Korean military forces would be ready to assume wartime operational control of the U.S.-ROK Combined Forces Command and to what extent the South Korean military currently meets such conditions. Section 1319 required the Secretary of Defense to commission an independent study from a federally funded research and development center assessing, among other things, potential modifications to the U.S. Indo-Pacific Command that would affect U.S. Forces Korea, in response to the changing security environment. This report was due to Congress no later than 360 days after enactment of this act. H.R. 2670 passed the Senate on 12/13/2023 (87-13, Record Vote Number: 343) and passed the House on 12/14/2023 (310-118, Roll no. 723). The President signed the bill on 12/22/2023.

H.R. 7152 (Wexton), Korean American Divided Families National Registry Act. H.R. 7152 would have required the Department of State to identify Korean American families who wish to be reunited with family members who live in North Korea and establish a national registry of information on those families to (1) facilitate future reunions, and (2) provide a repository of information about such families. This bill was introduced in the House on 1/30/2024 and passed the House on 6/25/2024. It was received in the Senate and referred to the Senate Committee on Foreign Relations on 7/8/2024.

H.R. 6355 (Ryan), Never Forgotten Korean War POW Act. This bill would have amended the Combat Duty Pay Act of 1952 to require that former members of the uniformed services who were captured or entered a missing-in-action status during the Korean War while serving as a member of a combat unit in Korea receive combat pay for each month spent in a captured or missing-in-action status, rather than just a total of four months. H.R. 6355 was introduced on 11/9/2023 and referred to the House Committee on Armed Services the same day.

H.R. 1369 (Sherman), Peace on the Korean Peninsula Act. The bill would have stated that it is the sense of Congress that the State Department should "pursue serious, urgent diplomatic engagement with North Korea and South Korea in pursuit of a binding peace agreement constituting a formal and final end to the state of war between North Korea, South Korea, and the United States." The bill would have required that within 180 days of enactment the Department of State report to Congress on a "clear roadmap" for achieving lasting peace on the Korean Peninsula. The bill would have required the Department of State to report to Congress a review of the restrictions on travel by U.S. nationals to North Korea, including whether such restrictions should be adjusted to allow travel to North Korea to attend a funeral, burial, or commemoration of a relative. H.R. 1369 was introduced 3/3/2023 and referred to the House Committee on Foreign Affairs.

H.R. 958 (Steel), To require certain reports and briefings relating to North Korea. H.R. 958 would have required the President to report to Congress relating to (1) arms trafficking involving North Korea, (2) operators of foreign airports and sea ports that fail to inspect cargo to or from North Korea, and (3) cooperation between North Korea and Iran. This bill also would have required the President to provide a briefing to Congress twice a year regarding measures to deny specialized financial messaging services to designated North Korean financial institutions. This bill was introduced in the House on 2/9/2023 and referred to the House Committee on Foreign Affairs the same day.

H.Res. 318 (Meng) / S.Res. 175 (Menendez), Recognizing the importance of the 70^th anniversary of the signing of the Mutual Defense Treaty between the United States and the Republic of Korea on October 1, 1953. This resolution recognized the 70^th anniversary of the signing of the Mutual Defense Treaty between the United States and South Korea. Affirming the importance of the U.S.-South Korean alliance as the "linchpin to safeguarding peace, security, and prosperity on the Korean Peninsula," the resolution welcomed President Yoon Suk-yeol to the United States. It also supported ongoing defense and security ties, called for continued promotion of human rights, and encouraged close cooperation between the United States, South Korea, and Japan. H.Res. 318 was introduced in the House on 4/24/2023 and referred to the House Committee on Foreign Affairs the same day. S.Res. 175 was submitted and agreed to in the Senate without amendment by Unanimous Consent on 4/26/2023.

H.Res. 1056 (Connolly) / S.Res. 545 (Sullivan), Recognizing the importance of trilateral cooperation among the United States, Japan, and South Korea. H.Res. 1056 was introduced on 3/5/2024 and agreed to by voice vote on 9/9/2024. S.Res. 545 was introduced on 2/8/2024 and referred to the Senate Committee on Foreign Relations on 2/8/2024.

H.Res. 620 (Williams) / S.Res. 186 (Sullivan), A resolution seeking justice for the Japanese citizens abducted by North Korea. This resolution would have called on North Korea to release any abducted foreign nationals, including those from Japan. It also would have urged North Korea to return the remains of deceased abductees, to make restitution, to apologize, and to permanently cease such activities. H.Res. 620 was introduced on 7/26/2023 and referred to the House Committee on Foreign Affairs the same day. S.Res. 186 was referred to the Senate Committee on Foreign Relations on 5/1/2023.

H.Res. 126 (Kim), Encouraging reunions of divided Korean-American families. The resolution would have called on the United States and North Korea to begin the process of reuniting Korean Americans with their immediate relatives in North Korea. H.Res. 126 was introduced on 2/14/2023 and referred to House Committee on Foreign Affairs.

Appendix B. Legislation Related to U.S.-South Korea Security Issues from the 116^th Congress

The 116^th Congress was particularly active on U.S.-South Korea alliance issues, amid reports that President Trump was considering withdrawing some or all U.S. troops from South Korea and bilateral defense cost-sharing negotiations had grown divisive.

P.L. 116-283, William M. (Mac) Thornberry National Defense Authorization Act for Fiscal Year 2021. Section 1258 prohibited the use of funds to reduce the 28,500 active-duty U.S. servicemembers on the Korean Peninsula until 90 days after the Secretary of Defense certifies to the congressional defense committees that (1) "such a reduction is in the national security interest of the United States and will not significantly undermine the security of United States allies in the region" and (2) "the Secretary [of Defense] has appropriately consulted with allies of the United States, including South Korea and Japan, regarding such a reduction." H.R. 6395 was passed by the House on 12/28/2020 (322-87, Roll no. 253); it was passed by the Senate on 01/01/2021 (Record Vote Number: 291); and signed by the President on 01/01/2021.

P.L. 116-92, National Defense Authorization Act for Fiscal Year 2020. Section 1254 prohibited the use of funds to reduce the 28,500 active-duty U.S. servicemembers on the Korean Peninsula until 90 days after the Secretary of Defense certifies to the congressional defense committees that (1) "the reduction is in the national security interest of the United States and will not significantly undermine the security of United States allies in the region" and (2) "the Secretary [of Defense] has appropriately consulted with allies of the United States, including South Korea and Japan, regarding such a reduction." Section 1256 expressed the sense of Congress that the United States "remains committed" to the U.S.-ROK alliance as "essential to the peace and stability in the Indo-Pacific region." Furthermore, Congress stated in this section that U.S.-ROK-Japan cooperation is necessary to fight piracy, conduct disaster relief efforts, and protect maritime security. Section 1257 expressed the sense of Congress that diplomacy, economic sanctions, and credible deterrence are "essential" to address North Korea's conventional threats and weapons of mass destruction program. Congress further stated that North Korea threatens U.S. forces on the Korean Peninsula and U.S. allies in the region, and that its recent missile tests were "destabilizing." S. 1790 was passed by the House on 12/11/2019 (377-48, Roll no. 672); it was passed by the Senate on 12/17/2019 (86-8, Record Vote Number: 400); and signed by the President on 12/20/2019.

H.R. 6639 (Khanna) / S. 4020 (Markey), No Unconstitutional War with North Korea Act of 2020. This bill would have prohibited the use of federal funds for military force in or against North Korea unless (1) Congress has declared war, (2) Congress has enacted specific statutory authority for such military force, or (3) the President is exercising powers as Commander-in-Chief in a national emergency stemming from an attack against the United States or the Armed Forces. H.R. 6639 was introduced in the House on 4/28/2020 and referred to the House Committee on Foreign Affairs. S. 4020 was introduced in the Senate on 6/22/2020 and referred to the Senate Committee on Foreign Relations.

H.R. 7234 (Bera) / S. 4018 (Markey), We Go Together Act. This bill would have required the President, before changing U.S. policy with respect to the U.S.-South Korea Mutual Defense Treaty, to provide Congress with (1) a detailed justification for the change, (2) a certification that the change is in the U.S. national interest, and (3) a certification that an alternative agreement or measure is in place to replace any lost capacity or benefits stemming from the change. H.R. 7234 was introduced in the House on 6/18/2020 and referred to the House Committee on Foreign Affairs. S. 4018 was introduced on 6/22/2020 and referred to the Senate Committee on Foreign Relations.

H.R. 4084 (Barr), Otto Warmbier North Korea Nuclear Sanctions Act of 2019. This bill would have imposed sanctions on North Korean financial institutions, companies, and certain North Korean individuals due to North Korea's "proliferation and testing of WMD." H.R. 4084 was introduced in the House on 7/26/2019 and referred to the House Committee on Financial Services.

H.R. 2949 (Engel) / S. 1658 (Menendez), North Korea Policy Oversight Act of 2019. The bill would have required the State Department to report to Congress on diplomatic engagement with and by North Korea. It also would have mandated the Department of State to brief Congress after every high-level U.S.-DPRK diplomatic meeting. Furthermore, this bill would have required the President to notify Congress within five days of entering into any agreement with North Korea regarding the DPRK's nuclear and missile programs. H.R. 2949 was introduced in the House on 5/23/2019 and referred to the House Committee on Foreign Affairs. S. 1658 was introduced in the Senate on 5/23/2019 and referred to the Senate Committee on Foreign Relations.

H.R. 2047 (Green) / S. 985 (Lee), Allied Burden Sharing Report Act of 2019. This bill would have required the Secretary of Defense to submit a report to Congress each year detailing "the activities of [South Korea and other countries] to contribute to military or stability operations in which the Armed Forces of the United States are a participant." The report would also have had to outline limitations placed by South Korea on using such contributions, and what the United States was doing to minimize those limitations. H.R. 2047 was introduced in the House on 4/3/2019 and referred to the House Committee on Foreign Affairs. S. 985 was introduced on 4/2/2019 and referred to the Senate Committee on Foreign Relations.

H.R. 889 (Gallagher), United States and Republic of Korea Alliance Support Act. This bill would have barred the Department of Defense from reducing the number of active-duty servicemembers deployed to South Korea below 22,000, unless DOD made certain certifications, including that such a reduction was in the interest of national security. H.R. 889 was introduced in the House on 1/30/2019 and referred to the House Committee on Armed Services.

S. 3395 (Hirono), Korean War Divided Families Reunification Act. This bill would have directed the Department of State to consult with South Korea and representatives of Korean Americans with family in North Korea on reunification efforts. S. 3395 was introduced in the Senate on 3/5/2020 and referred to the Senate Committee on Foreign Relations.

H.Res. 127 (Engel) / S.Res. 67 (Menendez), Expressing the sense of the House of Representatives/Senate on the importance and vitality of the United States alliances with Japan and the Republic of Korea, and our trilateral cooperation in the pursuit of shared interests. The resolution "reaffirm[ed] the commitment of the United States to defend" Japan and the Republic of Korea under their respective mutual defense treaties with the United States. H.Res. 127 was introduced in the House on 2/13/2019 and agreed to on 9/24/2019. S.Res. 67 was introduced in the Senate on 2/12/2019 and agreed to on 4/10/2019.

H.Res. 1016 (Wenstrup) / S.Res. 623 (Portman), Recognizing the 3^rd anniversary of the passing of Otto Frederick Warmbier and condemning the North Korean regime for their continued human rights abuses. This resolution expressed remembrance for the life of Otto Frederick Warmbier on the third anniversary of his death. The resolution condemned North Korea for his death and called for sanctions against North Korea to remain fully implemented until North Korea committed to the suspension of its proliferation of weapons of mass destruction. H.Res. 1016 was introduced in the House on 6/22/2020 and referred to the House Subcommittee on Asia, the Pacific and Nonproliferation on 7/13/2020. S.Res. 623 was introduced in the Senate on 6/16/2020 and agreed to by Unanimous Consent on 6/18/2020.

H.Res. 1012 (Bera) / S.Res. 615 (Gardner), Recognizing the 70^th anniversary of the outbreak of the Korean War and the transformation of the United States-South Korea alliance into a mutually beneficial, global partnership. This resolution reaffirmed the critical importance of the alliance between the United States and South Korea. The resolution encouraged coordination between the two countries in certain areas and emphasized that the United States Forces Korea remained prepared to counter third-party aggression. H.Res. 1012 was introduced in the House on 6/22/2020 and agreed to without objection on 11/18/2020. S.Res. 615 was introduced in the Senate on 6/11/2020 and referred to the Senate Committee on Foreign Relations.

H.Res. 809 (Suozzi) / S.Res. 152 (Lankford), Expressing the importance of the United States alliance with the Republic of Korea and the contributions of Korean Americans in the United States. This resolution "recognize[d] the vital role the alliance of the United States and the Republic of Korea plays in promoting peace and security in the Indo-Pacific region" and called for further strengthening of ties between the two countries. H.Res. 809 was introduced in the House on 1/24/2020 and agreed to without objection on 11/18/2020. S.Res. 152 was introduced in the Senate on 4/9/2019 and agreed to by Unanimous Consent on 1/8/2020.

S.Res. 435 (Risch), Reaffirming the importance of the General Security of Military Information Agreement between the Republic of Korea and Japan, and for other purposes. This resolution (1) reaffirmed the importance of the General Security of Military Information Agreement (GSOMIA) between South Korea and Japan; (2) encouraged South Korea and Japan to rebuild trust and pursue cooperation on mutual interests; and (3) expressed support for strengthened alliances between the United States, South Korea, and Japan. (The GSOMIA is an agreement that allows Japan and South Korea to directly share military intelligence with one another.) S.Res. 435 was introduced in the Senate on 11/20/2019 and agreed to in the Senate on 11/21/2019.

H.Res. 152 (Khanna), Calling for a formal end of the Korean war. This resolution would have "call[ed] for the conclusion of a binding peace agreement constituting a formal and final end to the state of war between North Korea, South Korea, and the United States." At the same time, it would have affirmed that such a binding peace agreement would not have any legal effect on the U.S.-ROK mutual defense treaty, which would "remain in force indefinitely." H.Res. 152 was introduced in the House on 2/26/2019 and referred to the House Committee on Foreign Affairs.

H.Res. 439 (Steube), Maintaining North Korea's seizure of the vessel USS Pueblo and its detention of the crew were in violation of international law and seeking the return of the USS Pueblo to the United States. This resolution would have maintained that the January 23, 1968, seizure by North Korea of the USS Pueblo and the detention of its crew violated international law, and sought the return of the USS Pueblo to the United States. H.Res. 439 was introduced in the House on 6/12/2019 and referred to the House Committee on Foreign Affairs.

Appendix C. U.S.-ROK Mutual Defense Treaty

Footnotes

1.	Defense Casualty Analysis System, "U.S. Military Casualties—Korean War Casualty Summary," https://dcas.dmdc.osd.mil/dcas/app/conflictCasualties/korea/koreaSum.
2.	United Nations Command, "Armistice Negotiations," https://www.unc.mil/History/1951-1953-Armistice-Negotiations/.
3.	U.S. Forces Korea, "Mutual Defense Treaty Between the United States and the Republic of Korea; October 1, 1953," https://www.usfk.mil/portals/105/documents/sofa/h_mutual%20defense%20treaty_1953.pdf. See Appendix C for full text of the U.S.-ROK Mutual Defense Treaty.
4.	U.S. Forces Korea, "Mutual Defense Treaty Between the United States and the Republic of Korea; October 1, 1953."
5.	U.S. Department of State, "U.S. Security Cooperation With the Republic of Korea (ROK)," Fact Sheet, January 20, 2025.
6.	Ministry of National Defense of the Republic of Korea, "2022 Defense White Paper."
7.	U.S. Army, "History of U.S. Army Garrison Humphreys," https://home.army.mil/humphreys/about/history.
8.	"South Korea: Section 3—Force Structures," Forecast International 2024.
9.	D. Sean Barnett et al., "North Korean Conventional Artillery," Rand Corporation, August 6, 2020.
10.	Defense Intelligence Agency, 2025 Worldwide Threat Assessment, May 11, 2025, pp. 20-21.
11.	Defense Intelligence Agency, 2025 Worldwide Threat Assessment, May 11, 2025, pp. 20-21.
12.	"North Korea Ramps Up Criticism Against South Korea-U.S. Drills, but No Mention of Missile Launch," Korea JoonAng Daily, March 11, 2025.
13.	U.S. Department of Defense, "Obama, South Korean President Reaffirm U.S.-South Korea Alliance," September 6, 2016; Trump White House Archives, "Joint Press Release by the United States of America and the Republic of Korea," November 8, 2017; U.S. Embassy in the Republic of Korea, "Leaders' Joint Statement in Commemoration of the 70th Anniversary of the Alliance Between the U.S. and the ROK," April 27, 2023; The White House, "Joint Fact Sheet on President Donald J. Trump's Meeting with President Lee Jae Myung," November 13, 2025.
14.	The White House, "Joint Fact Sheet on President Donald J. Trump's Meeting with President Lee Jae Myung."
15.	U.S. Embassy in the Republic of Korea, "South Korean President Yoon Suk Yeol's Address to a Joint Session of U.S. Congress," April 28, 2023.
16.	U.S. Embassy in the Republic of Korea, "South Korean President Yoon Suk Yeol's Address to a Joint Session of U.S. Congress," April 28, 2023.
17.	The First Island Chain generally refers to islands running from Japan, Taiwan, parts of the Philippines, and Malaysia. The White House, "National Security Strategy of the United States of America," November 2025.
18.	U.S. Department of War, 2026 National Defense Strategy, January 23, 2026.
19.	See, generally, Atomic Energy Act of 1954, 42 U.S.C. §§2011, et seq. (P.L. 83-703), and CRS In Focus IF11999, AUKUS Nuclear Cooperation, by Paul K. Kerr and Mary Beth D. Nikitin.
20.	See, for example, Chad O'Carroll, "How US Forces Korea Is Changing Its Tune on Mission to Counter North Korea," NKNews, June 12, 2025.
21.	The White House, "Fact Sheets Joint Fact Sheet on President Donald J. Trump's Meeting with President Lee Jae Myung," November 13, 2025; "Statesmen's Forum: His Excellency Lee Jae Myung, President of the Republic of Korea," transcript of remarks, Center for Strategic and International Studies, August 25, 2025.
22.	Section 1268 deals with plans to transfer wartime operational control (OPCON). Section 1271 touches on U.S.-ROK-Japan trilateral defense cooperation. For more, see "Chain of Command/Wartime Operational Control" and "U.S.-ROK-Japan Trilateral Cooperation" sections of this report.
23.	Kester Abbott, "What Does Lee Jae Myung's Victory Mean for South Korea's Indo-Pacific Strategy, and for Australia?" United States Studies Centre, June 26, 2025; The Asan Institute for Policy Studies, "South Koreans and Their Neighbors 2025," April 28, 2025.
24.	The Asan Institute for Policy Studies, "South Koreans and Their Neighbors 2025," April 28, 2025.
25.	Yul Sohn, "The Future of Korean Democracy and Institutional Reform] Polarized Politics, Fissured Diplomacy: How Partisanship Imperils South Korea's Foreign Policy," East Asia Institute, April 8, 2025, https://www.eai.or.kr/press/press_01_view.php?no=11257; Darcie Draudt-Véjares, The Transformation of South Korean Progressive Foreign Policy, Carnegie Endowment for International Peace, May 29, 2025.
26.	Darcie Draudt-Véjares, The Transformation of South Korean Progressive Foreign Policy, Carnegie Endowment for International Peace, May 29, 2025.
27.	United States Forces Korea, "Combined Forces Command," https://www.usfk.mil/About/CFC/.
28.	Congressional Record—Senate, daily edition, vol. 170, no. 149 (September 24, 2024).
29.	A "subordinate unified command" refers to a command that a Unified Combatant Commander (in this instance, the Commander, USINDOPACOM) establishes to manage particular missions or operations on a permanent basis, comprising forces from at least two military services. For more information, see https://www.armed-services.senate.gov/imo/media/doc/brunson_apq_responses.pdf.
30.	The U.S. Secretary of Defense is using "Secretary of War" as a "secondary title" under Executive Order 14347 dated September 5, 2025. For more on USINDOPACOM, see U.S. Indo-Pacific Command, "About USINDOPACOM," https://www.pacom.mil/About-USINDOPACOM/.
31.	United States Eighth Army, https://8tharmy.korea.army.mil/site/.
32.	United States Seventh Air Force, https://www.7af.pacaf.af.mil/About-Us/.
33.	U.S. Navy Region Korea, https://cnrk.cnic.navy.mil/.
34.	From 1910 to 1945, Japan colonized the Korean Peninsula. After Japan's defeat in World War II in 1945, the United States and the Soviet Union agreed to divide the Korean Peninsula, with each controlling roughly half. The 38th parallel became the demarcation line between the two occupation zones. Both the United States and the Soviet Union installed their own leaders—Syngman Rhee in the south, and Kim Il-Sung in the north. Mutual mistrust prevented the holding of elections meant to decide the leader of the entire peninsula. For more information, see United Nations Command, "History of the Korean War," and United States National Archives, "US Enters the Korean Conflict," https://www.archives.gov/education/lessons/korean-conflict#background.
35.	United Nations Command, UNSC Resolutions 83 and 84, https://docs.un.org/en/S/RES/83(1950) and https://docs.un.org/en/S/RES/85(1950).
36.	U.S. Department of Defense, "Long Diplomatic Wrangling Finally Led to Korean Armistice 70 Years Ago," July 24, 2023.
37.	United Nations Command, "Unified in Purpose," https://www.unc.mil/About/Our-Role/; CRS interview with U.S. Forces Korea official, April 30, 2025.
38.	United Nations Command, "Military Armistice Commission—Secretariat."
39.	United Nations Command, "United Nations Command—Rear."
40.	United Nations Command, "Unified in Purpose," https://www.unc.mil/About/Our-Role/; UNC Member States include: Australia, Belgium, Canada, Colombia, Denmark, France, Germany, Greece, Italy, Netherlands, New Zealand, Norway, Philippines, South Africa, Thailand, Türkiye (Turkey), the United Kingdom, and the United States. For more information, see https://www.war.gov/News/Releases/Release/article/3587434/republic-of-korea-and-united-nations-command-member-states-defense-ministerial/ and https://www.usfk.mil/Media/Press-Products/Press-Releases/Article/3859125/germany-joins-united-nations-command/.
41.	United Nations Command, "United Nations Command—Rear," https://www.unc.mil/Organization/UNC-Rear/.
42.	United States Forces Korea, "Combined Forces Command," https://www.usfk.mil/About/CFC/; CRS interview with U.S. Forces Korea official, April 30, 2025.
43.	CRS interview with U.S. Forces Korea official, April 30, 2025.
44.	Shawn Creamer, "Theater-Level Command and Alliance Decision Making Architecture in Korea," International Council on Korean Studies, pp. 7-11, http://icks.org/data/ijks/1498534150_add_file_3.pdf.
45.	Xiao Liang et al., "Trends in World Military Expenditure, 2024," Stockholm International Peace Research Institute, April 2025.
46.	U.S. Department of Commerce, "South Korea Country Commercial Guide: Defense Industry Equipment," December 5, 2023, https://www.trade.gov/country-commercial-guides/south-korea-defense-industry-equipment.
47.	Hunter Slingbaum and Kaitlyn King, "Will South Korea's Defense Industry Boom Change U.S.-ROK Military Relations?" Stimson Center, August 19, 2024, https://www.stimson.org/2024/will-south-koreas-defense-industry-boom-change-u-s-rok-military-relations/.
48.	"Top 100 for 2025," Defense News, accessed March 5, 2026, https://people.defensenews.com/top-100/.
49.	U.S. Department of Commerce, "South Korea Country Commercial Guide: Defense Industry Equipment," December 5, 2023, https://www.trade.gov/country-commercial-guides/south-korea-defense-industry-equipment.
50.	Anna J. Park, "Lee Vows 'Bold Investments' to Elevate Korea to Top-Tier Defense Power," The Korea Times, October 20, 2025.
51.	State Department, "U.S. Security Cooperation with the Republic of Korea (ROK)," January 20, 2025.
52.	The White House, "Joint Fact Sheet on President Donald J. Trump's Meeting with President Lee Jae Myung," November 13, 2025.
53.	Larry Niksch, "Potential Sources of Opposition to a U.S. Troop Withdrawal from South Korea," National Committee on North Korea (NCNK), April 2019, https://www.ncnk.org/sites/default/files/issue-briefs/Opposition_US_Troop_Withdrawal_South_Korea.pdf; Dr. Tim Kane, "U.S. Troop Deployments, 1950-2023," American Lyceum, November 2024, https://www.ustroopdeployments.com/; U.S. Department of State, "U.S. Security Cooperation with the Republic of Korea (ROK)," fact sheet, January 20, 2025.
54.	Carol E. Lee et al., "Kelly Thinks He's Saving U.S. from Disaster, Calls Trump 'Idiot,' Say White House staffers," NBC News, May 1, 2018.
55.	Nancy Youssef et al., "U.S. Considers Withdrawing Thousands of Troops from South Korea," The Wall Street Journal, May 23, 2025.
56.	Sean Parnell, post on X, May 23, 2025; Victor Cha, "The Meaning of U.S. Troop Withdrawals from Korea," Center for Strategic and International Studies, June 2, 2025.
57.	Jooheon Kim and Shreyas Reddy, "What Trump's Improbable Bid for ROK Land Reveals About His North Korea Plans," NK News, August 26, 2025, https://www.nknews.org/2025/08/what-trumps-improbable-bid-for-rok-land-reveals-about-his-north-korea-plans/?t=1772732443773.
58.	U.S. Department of Defense, "57th Security Consultative Meeting Joint Communique," November 14, 2025.
59.	Daniel Post, "Renewing Its Vows: U.S. Commitment to the Defense of South Korea," Georgetown Journal of International Affairs, January 6, 2025.
60.	Victor Cha, "The Meaning of U.S. Troop Withdrawals from Korea."
61.	U.S. Department of Defense, "Remarks by Secretary of Defense Pete Hegseth at the 2025 Shangri-La Dialogue in Singapore," May 31, 2025.
62.	Doug Bandow, "Why Is America Still in South Korea?" Cato Institute, April 20, 2023, https://www.cato.org/commentary/why-america-still-south-korea.
63.	Karl Friedhoff, "US Troop Drawdown in South Korea Worth Considering," The Hill, February 2, 2019.
64.	See, for example, Thomas Marcesa, "Reducing U.S. Troops in South Korea Would Be 'Problematic,' Top Commander Warns," UPI, April 11, 2025.
65.	For example, Section 1254 of the FY2020 NDAA (P.L. 116-92) and Section 1258 of the FY2021 NDAA (P.L. 116-283) restricted the use of funds to reduce U.S. troops in South Korea below 28,500 until the Defense Department met certain conditions. Conversely, Section 8125 of the Department of Defense Appropriations Act of 1989 (P.L. 100-463) limits the number of active-duty U.S. forces in Japan and South Korea to 94,450 at the end of each fiscal year.
66.	Don Oberdorfer and Robert Carlin, The Two Koreas: A Contemporary History, 3rd ed. (Basic Books, 2013), pp. 84-108.
67.	Larry Niksch, "Potential Sources of Opposition," NCNK; Clint Work, US Troops in Korea: From History's Vantage Point," Stimson Center, May 8, 2018, https://www.38north.org/2018/05/cwork050818/.
68.	Mark Esper, "'I Want to Meet with the Taliban': Tales of Trump's Head-Scratching Diplomacy," Politico, May 9, 2022; U.S. Congress, House Committee on Foreign Affairs, Subcommittee on Asia and the Pacific and Nonproliferation, On the Eve of the Summit: Options for U.S. Diplomacy with North Korea, 116th Congress, 1st session, February 26, 2019, https://www.govinfo.gov/content/pkg/CHRG-116hhrg35364/pdf/CHRG-116hhrg35364.pdf. Jung Min-ho, "Pulling US Troops Out of Korea Was Trump's Second-Term Priority, Esper's Memoir Reveals," The Korea Times, June 16, 2022.
69.	For more, see CRS Report R45169, A Peace Treaty with North Korea?, by Emma Chanlett-Avery et al.
70.	See Section 1252 of the FY2022 NDAA (P.L. 117-81); Section 1265 of the FY2023 NDAA (P.L. 117-263); Section 1301 of the FY2024 NDAA (P.L. 118-31); and Section 1311 of the FY2025 NDAA (P.L. 118-159).
71.	U.S. Department of State, "United States and the Republic of Korea Launch Strategic Consultation for Allied Partnership," January 19, 2006, https://2001-2009.state.gov/r/pa/prs/ps/2006/59447.htm.
72.	"Presidents Agree to Redeploy U.S. Forces in Korea to Iraq," The Chosun Daily, May 18, 2004.
73.	Clint Work, "What's in a Tripwire: The Post-Cold War Transformation of the US Military Presence in Korea," Stimson Center, June 9, 2022, https://www.stimson.org/2022/whats-in-a-tripwire-the-post-cold-war-transformation-of-the-us-military-presence-in-korea/.
74.	Ministry of Foreign Affairs of the Republic of Korea, "Korea, US Upgrade Ties to 'Global Comprehensive Strategic Alliance,'" May 25, 2022, https://www.mofa.go.kr/eng/brd/m_5674/view.do?seq=320723.
75.	U.S. Department of Defense, "Defense Vision of the U.S.-ROK Alliance," November 13, 2023.
76.	The White House, "Joint Fact Sheet on President Donald J. Trump's Meeting with President Lee Jae Myung," November 13, 2025; U.S. Department of Defense, "57th Security Consultative Meeting Joint Communique," November 14, 2025.
77.	See, for example, "US Senator Says Congress Will Review Shipbuilding Reforms After Lee-Trump Summit," Yonhap, August 21, 2025, https://www.koreatimes.co.kr/southkorea/politics/20250820/us-senator-says-congress-will-review-shipbuilding-reforms-after-lee-trump-summit.
78.	Kook-hee Park and Seo-young Kim, "USFK Chief Denies Troop Cut in S. Korea, Reaffirms Regional Deployment Flexibility," The Chosun Daily, May 29, 2025.
79.	"Hints Dropped That USFK Might Have to Help Defend Taiwan," Korea JoongAng Daily, September 27, 2022.
80.	U.S. Department of Defense, "Secretary of Defense Pete Hegseth Delivers Keynote Address at Special Operations Forces Week 2025," May 6, 2025; Lee Hyo-jin, "S. Korea on Edge as US Eyes USFK Role in Taiwan Contingencies," The Korea Times, March 31, 2025; Andrew Yeo, Korea Pro Podcast, December 3, 2024, https://koreapro.org/category/south-korea-news-podcast/latest/special-episode-with-andrew-yeo-trump-2-0-and-alliance-challenges-ep-50/2207357/?t=1741979519824.
81.	U.S. Air Force, Kunsan Air Base, "431st Expeditionary Reconnaissance Squadron Activates, Hosts Assumptions of Command," September 29, 2025.
82.	Brad Lendon, "US Establishes New Reaper Drone Unit 250 Miles from China," CNN, September 30, 2025.
83.	Jeongmin Kim and Joon Ha Park, "What North Korea Stands to Lose If US Forces Korea Expands Mission to China," NK News, May 1, 2025; Andrew Yeo and Hanna Foreman, "Is South Korea Ready to Define Its Role in a Taiwan Strait Contingency?" Brookings Institution, March 28, 2025.
84.	Clint Work, "Seoul's Dilemma in the Face of a New Sole Pacing Threat and Scenario," Korea Economic Institute, April 2, 2025.
85.	"US Expert Not Ruling Out Possible Change in USFK Force Posture in Next 3 Years," The Korea Herald, November 21, 2025.
86.	Bruce Klingner, "South Korea Cannot Afford to Sit Out Taiwan Contingencies," Heritage Foundation, October 30, 2024, https://www.heritage.org/china/report/south-korea-cannot-afford-sit-out-taiwan-contingencies; Clint Work, "Siloed No More: The U.S.-ROK Alliance and a Taiwan Conflict," Korean Economic Institute of America, March 31, 2025, https://keia.org/publication/siloed-no-more-the-u-s-rok-alliance-and-a-taiwan-conflict/.
87.	Bruce Klingner, "South Korea Cannot Afford to Sit Out Taiwan Contingencies," Heritage Foundation, October 30, 2024, https://www.heritage.org/china/report/south-korea-cannot-afford-sit-out-taiwan-contingencies.
88.	Fareed Zakaria, CNN, September 25, 2022, https://transcripts.cnn.com/show/fzgps/date/2022-09-25/segment/01.
89.	Charlie Campbell, "Exclusive: Lee Jae-myung Aims to Steer South Korea Past Its Moment of Crisis and Mounting Challenges," Time Magazine, May 29, 2025.
90.	John Lee, "Nuclear Submarines Force Issue of How Far Seoul Publicly Aligns with US Goals," Korea Pro, November 21, 2025.
91.	United Nations Comtrade Database, 2024.
92.	William Gallo, "Caught in US-China Rivalry, South Korea Inches Toward Washington," Voice of America, June 5, 2023.
93.	Russell Hsaio, "Taiwan and South Korea Enhancing Their Engagement as Chinese Aggression Intensifies," Global Taiwan Institute, September 20, 2023.
94.	The White House, "U.S.-ROK Leaders' Joint Statement," May 21, 2021; "United States-Republic of Korea Leaders' Joint Statement," May 21, 2022; "Leaders' Joint Statement in Commemoration of the 70th Anniversary of the Alliance Between the United States of America and the Republic of Korea," April 26, 2023.
95.	"South Korea's Yoon Opens Door for Possible Military Aid to Ukraine," Reuters, April 19, 2023.
96.	Yoo Jee-ho, "Lee Says Summit with China's Xi Put Bilateral Ties Back on Track," Yonhap News Agency, November 2, 2025.
97.	U.S. Department of State, "U.S. Security Cooperation with the Republic of Korea (ROK)," January 20, 2025.
98.	U.S. Government Accountability Office (GAO), BURDEN SHARING: Benefits and Costs Associated with the U.S. Military, GAO-21-270, March 17, 2021, p. 17, https://www.gao.gov/assets/gao-21-425.pdf.
99.	Won Gon Park, "A Challenge for the ROK-U.S. Alliance: Defense Cost-Sharing," East Asia Institute, July 2013.
100.	U.S. Forces Koreas, "U.S.-ROK Status of Forces Agreement," https://www.usfk.mil/Portals/105/Documents/Contracting/Contractor%20Links%20Sept%2015/US-ROK%20SOFA_1966-67.pdf#page=5.
101.	Phil Stewart and Idrees Ali, "Exclusive: Inside Trump's Standoff with South Korea over Defense Costs," Reuters, April 11, 2020, https://www.reuters.com/article/world/exclusive-inside-trumps-standoff-with-south-korea-over-defense-costs-idUSKCN21T051/.
102.	Nicole Gaouette, "Trump Hikes Price Tag for US Forces in Korea Almost 400% as Seoul Questions Alliance," CNN, November 15, 2019, https://www.cnn.com/2019/11/14/politics/trump-south-korea-troops-price-hike/index.html.
103.	U.S. Department of State, "Agreement Between the United States of America and the Republic of Korea (Special Measures Agreement)," March 8, 2019, https://www.state.gov/wp-content/uploads/2019/06/19-405-Korea-SMA.pdf.
104.	Office of U.S. Congresswoman Grace Meng, Letter from Congresswoman Meng to Secretaries Pompeo and Esper, November 15, 2019, https://meng.house.gov/sites/evo-subsites/meng-evo.house.gov/files/Meng%20Letter%20to%20Pompeo%20and%20Esper.pdf; Office of Congressman Ami Bera, Letter from Congressman Bera to Secretaries Pompeo and Esper, March 11, 2020.
105.	Kim Gamel, "Furlough of South Korean Workers Would Have 'Negative Impact' on Military Operations and Readiness, USFK Commander Says," Stars and Stripes, February 24, 2020, https://www.stripes.com/theaters/asia_pacific/furlough-of-south-korean-workers-would-have-negative-impact-on-military-operations-and-readiness-usfk-commander-says-1.620021.
106.	U.S. Department of State, "Agreement Between the United States of America and the Republic of Korea (Special Measures Agreement)," April 8, 2021, https://www.state.gov/wp-content/uploads/2021/10/21-901-Korea-Defense-SMA.pdf.
107.	U.S. Department of State, "ROK Special Measures Agreement Consultations," October 4, 2024.
108.	"New Defense Cost-Sharing Deal with U.S. Officially Takes Effect," The Korea Times, November 29, 2024.
109.	Kim Seung-yeon, "S. Korea, U.S. Sign Defense Cost-Sharing Deal Ahead of U.S. Elections," November 4, 2024, Yonhap News Agency, https://en.yna.co.kr/view/AEN20241104010200315.
110.	U.S. Department of State, "Agreement Between the United States of America and the Republic of Korea (Special Measures Agreement)," signed November 4, 2024, https://www.state.gov/wp-content/uploads/2025/05/24-1129-Korea-Defense-Special-Measures-Agreement.pdf#page=5.
111.	U.S. Department of State, "Agreement Between the United States of America and the Republic of Korea (Special Measures Agreement)," signed April 8, 2021, https://www.state.gov/wp-content/uploads/2021/10/21-901-Korea-Defense-SMA.pdf.
112.	Song Sang-ho, "New S. Korea-U.S. Defense Cost Deal Adds Stability to Alliance, but Trump Question Lingers: Experts," Yonhap News Agency, October 5, 2024.
113.	The White House, "Joint Fact Sheet on President Donald J. Trump's Meeting with President Lee Jae Myung," November 13, 2025.
114.	"Seoul's Pledge of $33 Billion in Support to USFK Shows Growing Defense Burden Under Trump," Hankyoreh, November 17, 2025.
115.	U.S. Government Accountability Office (GAO), BURDEN SHARING: Benefits and Costs Associated with the U.S. Military, GAO-21-270, March 17, 2021, p. 41.
116.	In the early years of the U.S.-ROK alliance, all U.S. and ROK forces were under the operational control of the USFK commander. In 1994, the allies agreed to transfer armistice (non-wartime) operational control of the ROK forces to a South Korean general.
117.	CRS interview with U.S. Forces Korea official, April 30, 2025; Kathryn Botto, "Why Doesn't South Korea Have Full Control over Its Military?" Carnegie Endowment for International Peace, August 21, 2019.
118.	"Military Considerations for OPCON Transfer on the Korean Peninsula," Council on Foreign Relations, March 20, 2020, https://www.cfr.org/blog/military-considerations-opcon-transfer-korean-peninsula.
119.	Song Sang-ho, "Allies Rack Brains over OPCON Transfer," The Korea Herald, May 6, 2014.
120.	U.S. Department of Defense, "Joint Communiqué: The 46th ROK-U.S. Security Consultative Meeting," October 23, 2014.
121.	CRS interview with U.S. Forces Korea official, April 30, 2025.
122.	Ministry of Defense of the Republic of Korea, "2022 Defense White Paper," https://www.mnd.go.kr/user/mndEN/upload/pblictn/PBLICTNEBOOK_202307280406019810.pdf.
123.	U.S. Department of Defense, "56th Security Consultative Meeting Joint Communique," October 30, 2024, https://www.war.gov/News/Releases/Release/Article/3951794/56th-security-consultative-meeting-joint-communique/; Asami Asaki, The Wartime OPCON Transfer Issues and the U.S.-ROK Alliance, The National Institute for Defense Studies, September 2021, https://www.nids.mod.go.jp/english/publication/briefing/pdf/2021/briefing_e202109.pdf.
124.	Lami Kim, "A Hawkish Dove? President Moon Jae-in and South Korea's Military Buildup," War on the Rocks, September 15, 2021, https://warontherocks.com/2021/09/a-hawkish-dove-president-moon-jae-in-and-south-koreas-military-buildup/.
125.	Hwang Joo-young, "Lee Proposes Wartime OPCON Transfer by 2030," The Korea Herald, August 13, 2025; Jeongmin Kim, "South Korean Presidential Candidates' Defense Platforms Diverge by Ideology," Korea Pro, May 22, 2025.
126.	U.S. Department of Defense, "57th Security Consultative Meeting Joint Communique," November 14, 2025.
127.	Lami Kim, "A Hawkish Dove?" War on the Rocks; "Not a Sovereignty Issue: Understanding the Transition of Military Operational Control between the United States and South Korea," Institute for Security and Development Policy (ISP), April 2021, https://www.isdp.eu/publication/not-a-sovereignty-issue-understanding-the-transition-of-military-operational-control-between-the-united-states-and-south-korea/.
128.	Anna J. Park, "Is Korea Ready for OPCON transfer?" The Korea Times, March 6, 2025.
129.	"Not a Sovereignty Issue," ISP; "Military Considerations for OPCON Transfer," CFR.
130.	This section was co-authored with Mary Beth D. Nikitin, Specialist in Nonproliferation, Foreign Affairs, Defense, and Trade Division.
131.	U.S. Department of Defense, National Defense Strategy of the United States of America, Including the 2022 Nuclear Posture Review and the 2022 Missile Defense Review, October 27, 2022.
132.	U.S. Department of Defense, National Defense Strategy of the United States of America, Including the 2022 Nuclear Posture Review and the 2022 Missile Defense Review, October 27, 2022.
133.	See CRS In Focus IF12735, U.S. Extended Deterrence and Regional Nuclear Capabilities, by Anya L. Fink.
134.	See CRS In Focus IF10472, North Korea's Nuclear Weapons and Missile Programs, by Mary Beth D. Nikitin and Daniel M. Gettinger.
135.	CRS In Focus IF12645, The Terminal High Altitude Area Defense (THAAD) System, by Andrew Feickert.
136.	U.S. Department of Defense, "U.S. to Deploy THAAD Missile Battery to South Korea," July 8, 2016.
137.	United States Forces Korea, "MND and U.S. Joint Statement on THAAD Updates," PA-001-22, October 7, 2022.
138.	See CRS Report R44950, Redeploying U.S. Nuclear Weapons to South Korea: Background and Implications in Brief, by Amy F. Woolf and Emma Chanlett-Avery; Jennifer Ahn, "The Evolution of South Korea's Nuclear Weapons Policy Debate," Council on Foreign Relations, August 16, 2022.
139.	J. James Kim et al., "Asan Report: Fundamentals of South Korean Public Opinion on Foreign Policy and National Security," The Asan Institute for Policy Studies, September 2021; Toby Dalton, Karl Friedhoff and Lami Kim, "Thinking Nuclear: South Korean Attitudes on Nuclear Weapons: Public Opinion Survey," The Chicago Council on Global Affairs, February 21, 2022.
140.	Victor Cha, "Breaking Bad: South Korea's Nuclear Option," CSIS, April 2024.
141.	Jeongmin Kim, "Where South Korea's Candidates Stand on Foreign Policy: All You Need to Know," Korea Pro, May 30, 2025.
142.	Kim Tae-jun, "Lee Jae-myung Defends Nuclear Initiatives as Non-Proliferation Compliant," The Chosun Daily, December 3, 2025.
143.	U.S. Embassy in the Republic of Korea, "Washington Declaration," April 27, 2023, https://kr.usembassy.gov/042723-washington-declaration/.
144.	U.S. Embassy in the Republic of Korea, "Washington Declaration," April 27, 2023, https://kr.usembassy.gov/042723-washington-declaration/.
145.	U.S. Embassy and Consulate in the Republic of Korea, "Joint Readout of the Inaugural U.S.-ROK Nuclear Consultative Group Meeting," July 18, 2023.
146.	U.S. Embassy and Consulate in the Republic of Korea, "Washington Declaration," April 27, 2023.
147.	Reuters, "U.S. Nuclear-Armed Submarine Visits South Korea as Allies Talk War Planning," July 18, 2023.
148.	U.S. Department of Defense, "Joint Press Statement on the Fourth Nuclear Consultative Group Meeting," January 10, 2025.
149.	U.S. Department of Defense, "57th Security Consultative Meeting Joint Communique," November 14, 2025.
150.	U.S. Forces Korea, "Mutual Defense Treaty Between the United States and the Republic of Korea; October 1, 1953," https://www.usfk.mil/portals/105/documents/sofa/h_mutual%20defense%20treaty_1953.pdf.
151.	See, for example, S.Res. 175 and H.Res. 318.
152.	See House Armed Services Committee, "U.S. Military Posture and National Security Challenges in the Indo-Pacific Region," April 9, 2025, and Senate Armed Services Committee, "To Receive Testimony on the Posture of the United States Indo-Pacific Command and United States Forces Korea in Review of the Defense Authorization Request for Fiscal Year 2026 and the Future Years Defense Program," April 10, 2025.
153.	For example, in February 2019, when South Korea-Japan relations were entering a particularly tense phase, a bipartisan, bicameral group of lawmakers, including the chairmen and ranking members of the House Foreign Affairs Committee and Senate Foreign Relations Committee, co-sponsored a resolution (H.Res. 127 and S.Res. 67) affirming the importance of U.S.-South Korea-Japan trilateral cooperation.
154.	This section was prepared by Ronald O'Rourke, former Specialist in Naval Affairs, Foreign Affairs, Defense, and Trade Division.
155.	CRS Report RL32665, Navy Force Structure and Shipbuilding Plans: Background and Issues for Congress, by Ronald O'Rourke. See also CRS Testimony TE10110, The State of U.S. Shipbuilding, by Ronald O'Rourke (statement before Armed Services Committee, Seapower and Projection Forces Subcommittee, U.S. House of Representatives, March 11, 2025).
156.	See, for example, Zita Ballinger Fletcher, "Top US, South Korean Shipbuilders Partner to Bolster Vessel Production," Defense News, April 7, 20235; Sam LaGrone, "Naval Shipbuilder HII Signs Agreement with South Korean Shipyard Hyundai Heavy Industries," USNI News, April 7, 2025; Matthew Beinart, "HII, South Korea's HD Hyundai Heavy Industries Sign MoU For Accelerating Ship Production," Defense Daily, April 7, 2025; Mike Glenn, "Largest U.S., South Korean Shipbuilding Companies to Collaborate to Ramp up U.S. Ship Production," Washington Times, April 7, 2025; Brad Lendon, "US and South Korean Warship Makers Sign Deal That Could Help Narrow Naval Race with China," CNN, April 8, 2025. For an article discussing how the adoption of South Korean and Japanese shipbuilder best practices could improve U.S. Navy shipbuilding, see Peter E. Jaquith, "Asian vs. U.S. Warship Design, Production Engineering, and Construction Practice," Naval Engineers Journal, December 2019, pp. 55-58.
157.	Kan Hyeong-woo, "Korea Sails into US Shipbuilding with $150b MASGA Push," The Korea Herald, July 31, 2025; Lydia DePillis and Choe Sang-Hun, "South Korea Reaches Trade Deal with Trump," The New York Times, July 30, 2025.
158.	Heesu Lee, "Korea Expects $350 Billion US Fund to Be Less Than 5% Equity," Bloomberg, August 3, 2025.
159.	See, for example, Hanwha, "Hanwha Announces $5 Billion Philly Shipyard Investment as Part of South Korea's Commitment to US Shipbuilding Growth," August 27, 2025; Justin Katz, "Hanwha Closes $100M Deal to Take Over Philly Shipyard," Breaking Defense, December 19, 2024. See also Rich Abott, "Incoming Philly Shipyard Owners Aim to Bring It Back to 1940s Prominence Plus Incoming M&As and Partnerships," Defense Daily, October 24, 2024; John Grady, "New Philly Shipyard Owners Promise 'Big Time' Investment," USNI News, October 23 (updated October 24), 2024; Valerie Insinna, "New Hanwha Defense USA Exec Sets Sights on Navy Contracts for Philly Shipyard," Breaking Defense, October 10, 2025; Nick Wilson, "Hanwha Eyes Module Production Work at Newly Acquired Philly Shipyard," Inside Defense, October 10. 2024.
160.	See, for example, U.S. Forces Korea, "USNS Wally Schirra Completes Major Maintenance at South Korean Shipyard," March 12, 2025, https://www.usfk.mil/Media/Newsroom/News/Article/4119997/usns-wally-schirra-completes-major-maintenance-at-south-korean-shipyard/.
161.	See, for example, Chang Dong-woo, "U.S. Navy Secretary Hopes for More Cooperation with Korean Shipbuilders amid U.S. Shipbuilding Push," Yonhap, May 8, 2025; Joyce Lee, "South Korea's Hanwha Ocean Targets US Navy Orders as Trump Seeks Shipbuilding Ties," Reuters, May 5, 2025; "South Korea Offers to Build Five Aegis Destroyers per Year to Help the US Counter China at Sea," Army Recognition, April 11, 2025.
162.	See, for example, Tom Sharpe, "Trump Plans to Rebuild the US Navy in Korean Shipyards. We Already Know This Works Well," Telegraph (UK), January 9, 2025; Brian T. Di Mascio, "Foreign Shipyards Can Help the U.S. Navy Build Its Fleet," U.S. Naval Institute Proceedings, October 2024; Douglas Robb, "Japan, South Korea and the US Should Mirror AUKUS for Destroyers," Defense News, October 5, 2023; Ajeyo Basu, "US Navy Looking at Japan, South Korea to Counter China's Military Power," Firstpost, June 5, 2023; Brad Lendon, "These May Be the World's Best Warships. And They're Not American" CNN, June 3, 2023.
163.	Howard Altman, "Trump Considering Buying Foreign Ships to Make Up Gap with China," The War Zone, April 11, 2025; Song Sang-ho, "Trump Says U.S. May Buy 'Top-of-the-Line' Ships from 'Close' Countries," Yonhap, April 11, 2025.
164.	See for example, Choe Sang-Hun, "South Korea Hopes Shipbuilding Will Give It an Edge in Trade Talks," New York Times, April 17 (updated April 18), 2025; James JB Park, "South Korea's Dockyards: A New Factor in Korea-US Military Burden-Sharing," Diplomat, November 21, 2024; Kan Hyeong-woo, "Korean Shipbuilders Upbeat on Trump's Call for Collaboration," The Korea Herald, November 10, 2025.
165.	See, for example, Matthew Paxton, "Outsourcing the US Shipyard Industrial Base Will Outsource American Sovereignty," Breaking Defense, August 5, 2024.
166.	Office of the Director of National Intelligence, "Annual Threat Assessment of the U.S. Intelligence Community," March 2025.
167.	"Trump Says He Wants to Meet North Korea's Kim Jong Un During South Korean President's Visit," CNA, August 25, 2025, https://www.youtube.com/watch?v=8DqshoJD3rc.
168.	Julian Ryall, "South Korea Fears Being Sidelined by Trump-Kim Revival," DW, February 3, 2025.
169.	"Full Text: President Lee Jae-myung's June 4 Inaugural Address," Korea Pro, June 4, 2025.
170.	Bahk Eun-ji, "Seoul, Washington Diverge over Joint Drills as Korea Signals Flexibility, US Stresses Readiness," The Korea Times, December 14, 2025; Thomas Maresca, "Military Exercises 'Critically Important,' U.S. Forces Korea commander says," UPI, December 12, 2025.