U.S.-South Korea Alliance: Issues for Congress
Updated September 12, 2023
U.S.-South Korea Alliance: Issues for Congress
Background
uncertainty about U.S. security guarantees and heightened
South Korea (officially the Republic of Korea, or ROK) is
sense of vulnerability, some South Koreans have advocated
one of the United States’ most important military and
that the United State redeploy tactical nuclear weapons to
economic partners in Asia. The U.S.-ROK Mutual Defense
the country (the United States withdrew nuclear weapons
Treaty, signed in 1953 at the end of the Korean War,
from the Korean Peninsula in 1991). Some public opinion
commits the United States to help South Korea defend
polls suggest that a strong majority of South Koreans
itself, particularly from North Korea (officially the
support developing a domestic nuclear weapons capability.
Democratic People’s Republic of Korea, or DPRK). The
U.S. military has maintained a large troop presence in
In an apparent bid to reassure South Koreans skeptical of
South Korea since the end of the Korean War. Currently,
U.S. extended deterrence (the ability and commitment to
approximately 28,500 U.S. troops are based in the ROK,
deter nuclear threats against allies, sometimes referred to as
predominately U.S. Army personnel. Most U.S. troops in
the “nuclear umbrella”), the two governments issued what
the ROK are stationed at Camp Humphreys, which
they called the “Washington Declaration” during Yoon’s
underwent a major expansion in the 2010s and is the largest
April 2023 State Visit. The declaration articulated a pledge
U.S. overseas military base in the world. The tools
to enhance bilateral planning, exercises, and other
Congress uses to oversee and influence the U.S.-ROK
consultations related to nuclear deterrence. It also
include annual authorization and appropriations bills,
established a Nuclear Consultative Group, which met for
particularly the National Defense Authorization Act
the first time in June 2023. The Nuclear Consultative Group
(NDAA), and annual House and Senate Armed Service
is intended to align and advance efforts to bolster
Committee hearings involving the commander of U.S.
deterrence against DPRK nuclear threats, with a particular
Forces Korea.
emphasis on joint planning for ROK conventional support
to U.S. nuclear operations and on enhancing the visibility of
Major Alliance Developments since 2022
U.S. “strategic asset deployments” to the Peninsula.
The Biden Administration has committed to reinvigorate
Questions remain about the implementation and durability
the alliance and has found a willing partner in South Korean
of the Washington Declaration as South Koreans continue
President Yoon Suk-yeol, elected in March 2022. The
to debate the country’s future relationship to nuclear
alliance had been strained during the Trump
weapons.
Administration: President Trump’s periodic references to
withdrawing U.S. troops from the Peninsula, his criticism
The Camp David Trilateral Summit and the Future
of the value of alliances more broadly, and the expiration of
of the U.S.-South Korea-Japan Relationship
a burden-sharing deal in 2019 raised questions in South
In August 2023, Biden hosted Yoon and Japanese Prime
Korea about U.S. security commitments. Shortly after
Minister Fumio Kishida at Camp David for the first-ever
Biden took office, the two sides concluded a new cost-
standalone summit meeting between the leaders of the
sharing arrangement.
United States, Japan, and South Korea. At the meeting, the
three leaders announced several initiatives for a “new era of
The Biden and Yoon administrations have advanced several
trilateral partnership.” They agreed to: institutionalize
initiatives to strengthen the alliance and commemorate its
trilateral meetings at high levels, including an annual
70th anniversary in 2023. Whereas the alliance traditionally
leaders’ meeting to coordinate Indo-Pacific strategy;
has been focused on deterring North Korea and preparing
establish a three-way hotline for crisis response; and expand
for a potential attack from the North, the alliance has
trilateral military exercises. Biden praised Yoon and
widened its scope to cooperate on other regional and global
Kishida’s “courageous leadership in transforming relations
issues. In April 2023, Biden hosted Yoon for a State Visit,
between Japan and the ROK,” which have been perennially
and Yoon addressed a joint meeting of Congress. Since
fraught because of a territorial dispute and sensitive
2022, the alliance also has re-started and expanded large-
historical issues stemming from Japan’s colonization of the
scale bilateral military exercises. South Korea has joined
Korean Peninsula from 1910 to 1945. Some observers
the international campaign to pressure Russia through
question whether this unprecedented arrangement, which
sanctions and support for Ukraine, and has worked
the main ROK opposition party opposes, will survive
vigorously to improve frayed ties with Japan.
beyond the administrations of the current leaders.
The Washington Declaration and the Future of
Military Exercises and the DPRK
Extended Deterrence
The threat from North Korea has framed the alliance since
Since 2013, multiple North Korean nuclear weapon tests
its formation. (For more on the DPRK, see CRS In Focus
and missile tests have sharpened the DPRK’s threat to
IF10472, North Korea’s Nuclear Weapons and Missile
South Korea. In a sign of South Koreans’ increased
Programs, and CRS In Focus IF10246, U.S.-North Korea
https://crsreports.congress.gov
U.S.-South Korea Alliance: Issues for Congress
Relations.) Since the 1950s, the U.S. and ROK militaries
U.S. and ROK civilian authorities; neither side would
have conducted regular bilateral exercises to enhance their
relinquish command authority over their own troops.
capability as a joint force. The exercises facilitate readiness
and operational cohesion, but can also contribute to
The OPCON transfer, announced in 2006, twice delayed,
tensions on the Peninsula. Pyongyang has responded
and now on an indefinite “conditions-based” timeline,
angrily to drills, calling them “preparation for war.” When
would reflect the ROK’s advances in military strength since
the United States and South Korea have pursued diplomacy
the Korean War and is seen by many South Koreans as an
with Pyongyang, the alliance sometimes has scaled back
important tenet of ROK sovereignty. Yoon’s predecessor
military activities. For example, following the 2018 summit
Moon Jae-in had prioritized the transfer; Yoon reportedly
with North Korean Leader Kim Jong-un, then-President
has not pressed as forcefully to accelerate the transfer. In
Trump cancelled large-scale military exercises. In 2022, the
general, more progressive leaders (such as Moon) have
U.S. and ROK resumed large-scale in-person exercises.
favored greater autonomy for South Korea, and the ROK
military, within the alliance; conservative leaders have
Figure 1. U.S. Military Bases in South Korea
tended to be more comfortable with the status quo.
ROK Defense and Military Issues
In 2022, South Korea was the world’s 9th-largest defense
spender; spending about 2.7% of its GDP on defense. In
August 2023, the ROK Ministry of National Defense
announced a proposed 2024 defense budget of around $45
billion. If approved, this would represent a year-on-year
increase of 4.5%, marking a slight slowdown in growth
compared to general trends over the past decade. The ROK
is among the top purchasers of U.S. Foreign Military Sales
(FMS). From FY2018 to FY2022, FMS to South Korea
totaled $7.67 billion, making it the ninth-largest purchaser
during those years according to DOD’s historical sales data.
Source: Amber Wilhelm (CRS).
South Korea has a mature defense industry itself, funded in
part by massive increases in the value of defense exports
Cost-Sharing Negotiations
since the mid-2000s. From 2018 to 2022, South Korea was
Since 1991, South Korea has provided financial support to
the world’s 9th-largest exporter of major arms. The ROK
the alliance through periodically re-negotiated Special
government prohibits lethal weapons transfers to countries
Measures Agreements (SMAs) to offset the cost of
at war, but faces growing U.S. pressure to send arms to
stationing U.S. forces in Korea. SMA negotiations became
Ukraine. In 2023, Seoul reportedly began transferring
particularly contentious during the Trump Administration,
500,000 artillery rounds to the United States, which planned
which requested steep increases in ROK contributions.
to send them to Ukraine. The previous year, South Korea
Amid the impasse, the previous SMA expired in December
struck its largest-ever arms deal, selling tanks, aircraft, and
2019, leading to the furlough of about 4,500 Koreans who
other items reportedly valued at $13.7 billion to Poland;
worked on U.S. bases. After Biden’s 2021 inauguration, the
some of the equipment replaces weapons Poland had
two sides concluded a new five-year SMA, removing an
transferred to Ukraine from its own stocks.
irritant to the relationship. Under the agreement, South
Korea is to pay about $1 billion annually, representing an
Congress’s Role in the Alliance
increase of about 13.9% over previous SMAs.
Support for the alliance has been bipartisan, and Congress
has acted to restrain the executive branch’s ability to make
In the past, South Korea generally paid for 40%-50% (over
major changes to force structure on the Peninsula. For
$800 million annually) of the total non-personnel costs of
example, the NDAAs for FYs 2020 and 2021 (P.L. 116-92
maintaining the U.S. troop presence in South Korea. ROK
and P.L. 116-283) prohibited the use of funds to reduce
payments—a combination of in-kind and cash
U.S. forces deployed to South Korea below 28,500 until 90
contributions—fall into three categories: labor (salaries for
days after the Secretary of Defense certifies to Congress (1)
the Koreans who work on U.S. bases); logistics; and
that such a reduction is in the U.S. national interest and will
construction (by ROK firms for U.S. facilities). The ROK
not significantly undermine the security the U.S. allies in
government spent $9.7 billion, or about 90% of the total
the region and (2) that regional U.S. allies have been
cost, of the expansion of Camp Humphreys.
“appropriately consulted” on the proposed reduction. The
Senate-amended version of an FY2024 NDAA
Wartime Operational Control (OPCON) (incorporating S. 2226 into H.R. 2670) would require a
The alliance plans to transfer wartime operational control of
report on the conditions under which wartime OPCON
the U.S.-ROK Combined Forces Command (CFC) to an
would be transferred to the ROK and an assessment of the
ROK commander, with a U.S. deputy. Under the current
ROK’s progress toward meeting those conditions.
decades-long arrangement, designated ROK military units
would be under a U.S. commander—and a South Korean
Emma Chanlett-Avery, Specialist in Asian Affairs
deputy commander—in the event of war on the Peninsula.
Caitlin Campbell, Analyst in Asian Affairs
If wartime OPCON is transferred, a South Korean
commander would become CFC head, answering to both
https://crsreports.congress.gov
U.S.-South Korea Alliance: Issues for Congress
IF11388
Christina L. Arabia, Analyst in Security Assistance,
Security Cooperation and the Global Arms Trade
Disclaimer
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