December 10, 2019
U.S.-South Korea Alliance: Issues for Congress
Overview of Alliance
Agreement (CMA). The CMA establishes land, sea, and air
South Korea (officially the Republic of Korea, or ROK) is
buffer zones in the heavily armed Demilitarized Zone
considered one of the United States’ most important
(DMZ) that separates the two Koreas and around the
strategic and economic partners in Asia. The U.S.-ROK
maritime border, called the Northern Limit Line.
Mutual Defense Treaty, signed in 1953 at the end of the
Implementation of the CMA required U.S. military officials
Korean War, commits the United States to help South
to modify practices in the DMZ, including removing land
Korea defend itself, particularly from North Korea
mines and guard posts. While observers point to a marked
(officially the Democratic People’s Republic of Korea, or
reduction of tension in the DMZ, some critics maintain that
DPRK). South Korean troops have fought in U.S.-led
the CMA-mandated changes reduced alliance readiness
conflicts, including in Vietnam, Iraq, and Afghanistan. The
with little sacrifice in return from North Korea.
United States includes South Korea under its “nuclear
umbrella,” otherwise known as extended deterrence.
Figure 1. U.S. Forces Korea (USFK) Bases
The U.S. military has maintained a large troop presence in
South Korea since the end of the Korean War. Currently,
approximately 28,500 U.S. troops are based in the ROK,
predominately Army personnel. Camp Humphreys, which
will host most of the troops when completed, is the largest
U.S. overseas military base in the world.
The U.S.-ROK alliance is strained on several fronts.
President Trump’s periodic references to bringing U.S.
troops home from the Peninsula and his criticism of the
value of alliances more broadly have raised questions in
Seoul about U.S. security commitments. Contentious
burden-sharing negotiations face a December 31, 2019,
deadline, just as North Korea threatens to return to
provocations. South Korean President Moon Jae-in wants to

complete the long-delayed process to transfer operational
Source: Jane’s Sentinel Security Assessment - China and Northeast
control of ROK forces in wartime to a South Korean
Asia, date posted April 15, 2010.
general, which could lead to disagreements about the timing
and conditions for the transition. In addition, growing
Burden-Sharing Negotiations
differences in approach to dealing with North Korea and
Negotiations in late 2019 revealed sharp differences
China could put increased pressure on the alliance.
between Washington and Seoul on how much South Korea
The Alliance and DPRK Policy
should contribute to offset U.S. costs to station troops on
the peninsula. These negotiations on cost-sharing
The threat from North Korea has framed the alliance since
arrangements—known as the “Special Measures
its formation. For years, the two militaries conducted
Agreement” or SMA—generally occur every five years.
regular bilateral exercises, enhancing their capability as a
The current talks aim to renew the accord signed in
joint force in the event of the resumption of hostilities with
February 2019 that raised South Korea’s previous annual
the North. Under President Moon and President Trump both
contribution by approximately 8%. Press reports indicate
governments have pursued diplomacy with Pyongyang and
that the Trump Administration now is asking South Korea
the alliance has adjusted its activities. For example, at a
to increase its contribution by roughly 400%.
summit with North Korean Leader Kim Jong-un in
Singapore in June 2018, President Trump called for a
In the past, South Korea generally paid for 40-50% (over
cancellation of large-scale military exercises, declaring
$800 million annually) of the total non-personnel costs of
them “very expensive” and “provocative.” With the
maintaining the U.S. troop presence in South Korea. ROK
resumption of smaller, less public exercises in 2019, U.S.
payments—a combination of in-kind and cash
military officials assert that the alliance has maintained
contributions—fell into three categories: labor (salaries for
readiness, but some analysts warn that the reduction in joint
the Koreans who work on U.S. bases); logistics; and
exercises could damage alliance cohesion.
construction (by ROK firms for U.S. facilities). In the
current talks, the U.S. side added a new category of
In 2018, South Korea and North Korea signed a tension-
“readiness” that captures a variety of other costs. South
reduction agreement known as the Comprehensive Military
Korea has balked at the U.S. figure and many observers
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U.S.-South Korea Alliance: Issues for Congress
predict that Seoul will allow the current SMA to expire on
A large-scale reduction or full withdrawal of the troops
December 31, 2019, rather than meet the U.S. request. The
stationed in South Korea would reshape the U.S. military
SMA must be approved by the ROK National Assembly,
presence in the region, leaving Japan alone as the major
increasing political pressure on the ROK government.
host of U.S. forces in the region. China and Russia would
likely appreciate a reduction in U.S. troops, having long
South Korean officials point to Seoul’s contributions to the
criticized U.S. alliances as outdated and counter-productive.
alliance beyond the SMA agreement. Military expenditures
account for 2.6% of its GDP, the largest percentage among
South Korean Defense Budget and
all U.S. allies. The ROK government is paying $9.7 billion,
Defense Industry
or about 90% of the total cost of constructing Camp
Under Moon, South Korea has increased its defense budget
Humphreys, and is a top buyer of U.S. defense systems.
significantly. The government has requested a $440 billion
budget for FY2020, a 9.3% increase from 2019. This
The South Korean press has aggressively covered the SMA
follows a 7.6% increase in FY2017 and an 8.2% increase in
negotiations and the ROK public is aware of the U.S.
FY2018, the highest among OECD member countries. The
position. Although opinion polls have indicated enduring
increases aim to boost acquisitions, facilitate OPCON
support for the U.S. alliance among South Koreans, recent
transfer, and respond to South Korea’s demographic
surveys have revealed limitations: in a November 2019
challenges, which constrain its conscription forces.
poll, nearly 70% of South Koreans opposed paying more to
the United States even if it resulted in a reduction in U.S.
South Korea is among the top customers for U.S. Foreign
troops. A drop in public support for the U.S. troop presence
Military Sales (FMS). From 2008 to 2016, ROK FMS
could undercut the political viability of the alliance.
contracts with the United States totaled $15.7 billion, and
commercial acquisitions totaled $6.9 billion. Although
Operational Control (OPCON)
European and Israeli defense companies also compete for
Another focus for the alliance is an agreement to transfer
contracts, from 2008 to 2016, approximately 75% of South
wartime operational control to the South Korean military.
Korea’s total foreign defense purchases have come in the
Under the existing arrangement, South Korean soldiers
form of FMS and commercial sales from U.S. companies.
would be under U.S. command in the event of war on the
Among the U.S. systems that South Korea is acquiring
peninsula. In peacetime, the ROK military is responsible for
include Lockheed Martin F-35 Joint Strike Fighters,
national security. The plan to transfer OPCON, begun in
Boeing’s P-8 Poseidon aircraft, and Northrup Grumman’s
2007 and twice delayed, recognizes the ROK’s advances in
RQ-4 “Global Hawk” unmanned aerial vehicles.
economic and military strength since the Korean War and is
seen by many Koreans as important for ROK sovereignty.
South Korea also has developed indigenous capabilities by
allocating resources to defense research and development.
President Moon aims to complete the process before his
According to South Korea’s 2018 Defense White Paper, by
term expires in May 2022. The two sides established
2023 the “force enhancement” budget will account for more
conditions and benchmarks to demonstrate that the ROK
than 36% of total defense spending, up from about 31% in
can assume wartime OPCON, including improved ROK
2019. The spending increase is tied to Seoul’s strategic
capabilities to lead combined forces and counter the DPRK
objectives, including a plan to integrate missile defense and
nuclear and missile threat, and a security environment on
other capabilities more closely with U.S. systems.
the Peninsula conducive to a transfer. Significant progress
has been made on some, but some areas remain slower to
Congressional Involvement
follow. Some also point to the challenge of imposing a
Support for the alliance has been widely bipartisan, and
political deadline on a complex process of technically
many in Congress appear keen to restrain the President’s
assessing capabilities and gauging security conditions.
ability to make major changes to force structure in the
region. Section 1254 of the FY2020 National Defense
Regional Implications
Authorization Act (NDAA) Conference Report to
The U.S.-ROK alliance is part of the post-World War II
Accompany S. 1790 prohibits the use of funds to reduce
“hub and spoke” system of U.S. security relationships in the
U.S. forces deployed to South Korea below 28,500 until 90
Asia-Pacific. Although labeled a “lynchpin” of U.S.
days after the Secretary of Defense certifies to Congress (1)
presence in the region by U.S. officials, the U.S.-ROK
that such a reduction is in the U.S. national interest and will
alliance has focused most heavily on the defense of the
not significantly undermine the security the U.S. allies in
peninsula itself from North Korean threats.
the region and (2) that U.S. allies have been “appropriately
consulted” on the proposed reduction. The FY2020 NDAA
The United States has urged greater coordination with other
would also require a report on South Korea’s (and Japan’s)
U.S. partners, particularly Japan, in confronting DPRK
contributions to U.S. alliances, and a sense of Congress on
threats and countering China’s military rise. Trilateral
the continued U.S. commitment to its alliances with South
cooperation has been challenging because of poor relations
Korea and Japan, as well trilateral cooperation between the
between Tokyo and Seoul. Although South Korea reversed
three countries.
its plan to withdraw from a military information sharing
agreement with Japan in November 2019, tensions in the
Emma Chanlett-Avery, Specialist in Asian Affairs
relationship remain. A rift in the U.S.-ROK alliance would
further impede effective trilateral security cooperation.
IF11388
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U.S.-South Korea Alliance: Issues for Congress


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