

Updated March 14, 2022
U.S.-South Korea Alliance: Issues for Congress
Overview of Alliance
Pyongyang, the alliance sometimes has scaled back its
South Korea (officially the Republic of Korea, or ROK) is
military activities. For example, at a summit with North
considered one of the United States’ most important
Korean Leader Kim Jong-un in Singapore in June 2018,
strategic and economic partners in Asia. The U.S.-ROK
former President Trump called for a cancellation of large-
Mutual Defense Treaty, signed in 1953 at the end of the
scale military exercises, declaring them “very expensive”
Korean War, commits the United States to help South
and “provocative.” Smaller, less public exercises resumed
Korea defend itself, particularly from North Korea
in 2019, but were later curtailed because of the coronavirus
(officially the Democratic People’s Republic of Korea, or
pandemic. In August 2021, the U.S. and ROK militaries
DPRK). South Korean troops have fought in U.S.-led
held joint drills, prompting North Korea to threaten to
conflicts, including in Vietnam, Iraq, and Afghanistan. The
accelerate its own military buildup.
United States includes South Korea under its “nuclear
umbrella,” otherwise known as extended deterrence. Most
In 2018, South Korea and North Korea signed a tension-
recently, South Korea has responded to Russian aggression
reduction agreement known as the Comprehensive Military
in the Ukraine with a range of sanctions and other punitive
Agreement (CMA). The CMA established land, sea, and air
measures.
buffer zones in the heavily armed Demilitarized Zone
(DMZ) that separates the two Koreas and around the
The U.S. military has maintained a large troop presence in
maritime border, called the Northern Limit Line.
South Korea since the end of the Korean War. Currently,
Implementation of the CMA required U.S. military officials
approximately 28,500 U.S. troops are based in the ROK,
to modify practices in the DMZ, including removing land
predominately Army personnel. Camp Humphreys, which
mines and guard posts. Observers pointed to a marked
will host most of the troops when it is completed, is the
reduction of tension in the DMZ, but North Korea has
largest U.S. overseas military base in the world.
failed to uphold much of its side of the agreement.
The Biden Administration has committed to reinvigorate
Figure 1. U.S. Forces Korea (USFK) Bases
the U.S.-ROK alliance after years of strain under the Trump
Administration. Former President Trump’s periodic
references to bringing U.S. troops home from the Peninsula,
his criticism of the value of alliances more broadly, and the
expiration of a burden-sharing deal in 2019 raised questions
in South Korea about U.S. security commitments. Despite
agreement on a new cost-sharing arrangement shortly after
Biden took office, the alliance faces a number of
challenges, including implementing an agreement to
transfer wartime operational control, deciding when and at
what scale to hold military exercises, and possibly pursuing
more robust trilateral cooperation with Japan. In addition,
different approaches to dealing with North Korea and China
may put increased pressure on the alliance. The election of
conservative politician Yoon Seok-youl as president in
March 2022 indicates to many analysts that U.S. and ROK
approaches to the alliance may come into greater alignment
Source: Jane’s Sentinel Security Assessment - China and Northeast
than under current president President Moon Jae-in, a
Asia, date posted April 15, 2010.
progressive politician whose term expires in May 2022.
The Alliance and DPRK Policy
Regional Issues
The U.S.-ROK alliance is part of the post-World War II
The threat from North Korea has framed the alliance since
“hub and spoke” system of U.S. security relationships in the
its formation in 1953. For years, the two militaries
Asia-Pacific. Although labeled a “lynchpin” of U.S.
conducted regular bilateral exercises, enhancing their
presence in the region by U.S. officials, the U.S.-ROK
capability as a joint force in the event of the resumption of
alliance has focused most heavily on the defense of the
hostilities with the North. The exercises facilitate
ROK itself from North Korean threats. Although Biden and
operational cohesion, but can also contribute to tensions on
Moon have supported globalizing the alliance, questions
the Peninsula. Pyongyang has responded angrily to alliance
remain about whether South Korea will join efforts that
drills, calling them “preparation for war.” When the United
challenge China or sign on for partnerships such as the
States and South Korea have pursued diplomacy with
Quadrilateral Security Dialogue (“the Quad”) among the
https://crsreports.congress.gov
U.S.-South Korea Alliance: Issues for Congress
United States, India, Japan, and Australia because of
improved ROK capabilities to lead combined forces and
Chinese objections. The United States has urged greater
counter DPRK threats, and a security environment
coordination with other U.S. partners, particularly Japan, in
conducive to a transfer. Significant progress has been made
confronting DPRK threats and countering China’s military
on some areas, but others remain slower to follow.
rise. Despite Biden Administration entreaties to strengthen
trilateral cooperation, poor relations between Tokyo and
South Korean Defense and Military
Seoul have stymied many efforts. Although South Korea
Issues
reversed its plan to withdraw from a military information
In 2020, South Korea had the 10th-largest defense spending
sharing agreement with Japan in November 2019, tensions
in the world, constituting about 2.8% of its GDP. Under a
in the relationship remain. President-elect Yoon has
program known as Defense Reform 2.0, South Korea is
promised to improve ties with Japan, and to seek to
investing heavily in new military equipment, particularly
participate in and perhaps eventually join the Quad.
for its missile defense program. In December 2021, South
Korea’s National Assembly approved a FY2022 defense
Burden-Sharing Negotiations
budget of $46.3 billion. This represented a 3.4% increase
Since 1991, South Korea has provided financial support to
from the FY2021 budget, and followed a 7.6% increase in
the alliance through a series of Special Measures
FY2017 and an 8.2% increase in FY2018. The increases
Agreements (SMAs) to offset the cost of stationing U.S.
aim to boost acquisitions, facilitate the OPCON transfer,
forces in Korea. SMA negotiations generally occur every
and respond to the country’s demographic challenges,
five years. These talks are often contentious, and they
which constrain its conscription forces. The moves also
became particularly divisive during the Trump
reflect a response to North Korea’s military advancements
Administration when Washington requested steep increases
and a long-standing desire by progressive South Korean
in ROK contributions. After signing a one-year stop-gap
leaders, including Moon, to expand South Korea’s
measure in February 2019, the pact expired in December
influence over military matters on the Korean Peninsula.
2019, leading to the furlough of about 4,500 Koreans who
President-elect Yoon has said he will continue military
worked on U.S. bases. The Biden Administration concluded
investments, particularly in missile defense.
a new five-year agreement in March 2021, removing an
irritant to the relationship. Under the agreement, South
South Korea has a mature defense industry, which the
Korea will pay about $1 billion annually, representing an
government has advanced in the past decade through
increase of about 13.9% over previous SMAs.
industrial collaboration, defense offsets, and targeted efforts
to acquire sophisticated technologies and expertise. Seoul
In the past, South Korea generally paid for 40-50% (over
also is among the top customers for U.S. Foreign Military
$800 million annually) of the total non-personnel costs of
Sales (FMS). From FY2017 to FY2020, South Korean FMS
maintaining the U.S. troop presence in South Korea. ROK
contracts with the United States totaled $5.95 billion,
payments—a combination of in-kind and cash
making it the tenth-largest recipient during those years. For
contributions—fell into three categories: labor (salaries for
years, South Korean officials have voiced an interest in
the Koreans who work on U.S. bases); logistics; and
acquiring or developing nuclear-powered submarines. The
construction (by ROK firms for U.S. facilities). South
Moon government raised this ambition after the surprise
Korean officials point to Seoul’s contributions to the
September 2021 announcement that the United States
alliance beyond the SMA agreement. Military expenditures
would help Australia develop a nuclear-powered submarine
account for 2.6% of its GDP, the largest percentage among
capability in cooperation with the United Kingdom. The
all U.S. allies. The ROK government is spending $9.7
United States has pushed back on South Korean calls for
billion, or about 90% of the total cost of construction, for
acquiring this capability, citing proliferation concerns.
Camp Humphreys, and is a top buyer of U.S. arms.
Congressional Involvement
Operational Control (OPCON)
Support for the alliance has been bipartisan, and many in
Another focus for the alliance is an agreement to transfer
Congress appear keen to restrain the President’s ability to
wartime operational control to the South Korean military.
make major changes to force structure in the region. Section
Under the existing arrangement, South Korean soldiers
1254 of the FY2020 NDAA (P.L. 116-92) and Section 1258
would be under U.S. command in the event of war on the
of the FY2021 NDAA (P.L. 116-283) prohibited the use of
peninsula. (In peacetime, the ROK military is responsible
funds to reduce U.S. forces deployed to South Korea below
for national security.) The plan to transfer OPCON, begun
28,500 until 90 days after the Secretary of Defense certifies
in 2007 and twice delayed, reflects the ROK’s advances in
to Congress (1) that such a reduction is in the U.S. national
economic and military strength since the Korean War and is
interest and will not significantly undermine the security the
seen by many Koreans as important for ROK sovereignty.
U.S. allies in the region and (2) that U.S. allies have been
“appropriately consulted” on the proposed reduction.
President Moon, like other progressive leaders before him,
Section 1252 of the FY2022 NDAA (P.L. 117-81) included
wanted to complete the long-delayed process to transfer
a sense of Congress echoing the desire to maintain current
operational control of ROK forces in wartime to a South
force levels in the country.
Korean general, but that appears out of reach during his
term. President-elect Yoon may not emphasize OPCON,
Emma Chanlett-Avery, Specialist in Asian Affairs
following in the tradition of previous conservative
presidents. The two sides have set conditions and
IF11388
benchmarks to guide the transfer decision, including
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U.S.-South Korea Alliance: Issues for Congress
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