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