US Military Presence in South Korea: Bases, Costs, and Alliance Shifts

The United States keeps roughly 28,500 troops in South Korea under a 1953 mutual defense treaty, with South Korea paying about $1.13 billion a year to help cover the cost.¹² The US military presence in South Korea is one of the longest continuous overseas deployments in American history, anchored by Camp Humphreys — the largest US base outside the country — and aimed at deterring North Korea and stabilizing Northeast Asia.

Why American Troops Are Still There

North Korean forces crossed the 38th parallel on June 25, 1950, and the United States led a United Nations multinational force in the three-year war that followed.³ The fighting stopped on July 27, 1953, when commanders from the UN Command, North Korea, and the Chinese People’s Volunteer Army signed the Korean Armistice Agreement after 158 meetings at Kaesong and Panmunjom. The armistice created a ceasefire and the Demilitarized Zone but did not end the war. Peace talks in Geneva in 1954 produced no treaty. The peninsula technically remains at war, and the UN Command still holds responsibility for upholding the armistice.⁴

That unfinished conflict is the reason the American presence continued after 1953 and continues now. North Korea’s nuclear program keeps expanding. In late December 2025, state media reported Kim Jong Un inspecting a new 8,700-tonne nuclear-powered submarine designed to carry strategic guided missiles, and in early January 2026 North Korea test-fired several missiles, including hypersonic variants. Pyongyang formally abandoned its goal of peaceful reunification in December 2023 and has rejected dialogue conditioned on denuclearization.⁵

The Legal Basis

The Mutual Defense Treaty between the United States and the Republic of Korea was signed on October 1, 1953, and entered into force on November 17, 1954.⁶ Article IV gives the United States the right to station land, air, and sea forces in and around South Korean territory by mutual agreement. Article III obligates each country to respond to an armed attack in the Pacific area, subject to its own constitutional processes. The treaty runs indefinitely; either party can terminate it with one year’s notice.⁷ The US Senate ratified the treaty with an explicit understanding that the American defense obligation applies only to external armed attacks against territory under South Korean administrative control.

The day-to-day rules for American personnel come from the Status of Forces Agreement (SOFA), first signed on July 9, 1966, and effective February 9, 1967.⁸ SOFA covers criminal jurisdiction, tax and customs treatment, facility costs, and the requirement that US personnel respect Korean law. It was revised in 1991 and again in 2001 after high-profile crimes involving American service members prompted public pressure for stronger South Korean legal authority. The 2001 revision, ratified by the Korean National Assembly 120 to 40, allows South Korean authorities to take custody of US suspects at indictment for 12 serious crimes, including murder and rape.⁹

Who Is Stationed Where

United States Forces Korea (USFK), established July 1, 1957, is the umbrella command.¹⁰ The USFK commander also leads the United Nations Command and the Combined Forces Command, the joint US-South Korean wartime headquarters. That post is held by Gen. Xavier T. Brunson.¹

Camp Humphreys

Camp Humphreys, in Pyeongtaek about 50 miles south of Seoul, is the center of the American footprint. Following a 2004 land-swap agreement that consolidated forces from garrisons in and north of Seoul, the base grew from roughly 1,200 acres to nearly 3,500 acres at a cost of about $10.7 billion, roughly 90 percent of it paid by South Korea. Ground was broken in November 2007, and the project involved nearly 700 new construction projects, including schools, a hospital, and housing.¹¹ The installation now hosts the headquarters of USFK, the Combined Forces Command, the United Nations Command, the Eighth Army, and the 2nd Infantry Division.¹²

Army

The Eighth Army, based at Camp Humphreys, is the ground component and the largest service presence on the peninsula. Its main combat formation is the 2nd Infantry Division, run as a combined ROK-US division. Supporting units include the 35th Air Defense Artillery Brigade, which operates Patriot and Avenger systems from Osan Air Base, the 19th Expeditionary Sustainment Command in Daegu, the 501st Military Intelligence Brigade, the 65th Medical Brigade, and the 1st Signal Brigade.¹³

Air Force

The Seventh Air Force, headquartered at Osan Air Base, oversees two F-16 fighter wings: the 51st Fighter Wing at Osan and the 8th Fighter Wing, the “Wolf Pack,” at Kunsan. Beginning in late 2024, the Seventh Air Force started a “Super Squadron” test that consolidates roughly 31 F-16s and about 1,000 airmen at Osan to see whether a larger centralized unit produces combat airpower more efficiently.¹⁴

Navy, Marines, and Special Operations

Commander, Naval Forces Korea (CNFK) is headquartered in Busan, with detachments in Chinhae and Pyeongtaek. Fleet Activities Chinhae is the only dedicated US Navy installation in Korea.¹⁵ CNFK works with the ROK Navy and coordinates with the US 7th Fleet in Yokosuka, Japan.¹⁶ Marine Forces Korea and Special Operations Command Korea keep smaller footprints than the Army and Air Force elements.

What South Korea Pays

Since the late 1980s, South Korea has helped pay to host American forces through a series of Special Measures Agreements. The 12th agreement, signed on November 4, 2024, covers 2026 through 2030.¹⁷ South Korea’s 2026 contribution is set at 1.5192 trillion Korean won, roughly $1.13 billion — an 8.3 percent increase from 2025. Annual increases from 2027 through 2030 are tied to South Korea’s consumer price index and capped at 5 percent. The money covers Korean labor on US bases, logistics support, and military construction. The agreement bars using the funds for US assets stationed outside Korea.¹⁸

Cost sharing has been a recurring source of friction. During his first term, President Trump reportedly sought a 400 percent increase in South Korean contributions. In April 2025, he suggested the cost of the American presence could factor into ongoing trade negotiations.¹⁹

Will the Troops Stay?

The question of whether to reduce or remove American troops keeps resurfacing. In May 2018, President Trump said a withdrawal was “not on the table” ahead of his summit with Kim Jong Un, while adding that “at some point into the future” he would like to bring forces home.²⁰

In May 2025, the Wall Street Journal reported that the Pentagon was developing an option to withdraw roughly 4,500 troops and move them to Guam as part of an informal North Korea policy review.²¹ The Pentagon denied the report. Spokesperson Sean Parnell said on May 23, 2025, that “reports that the DoD will reduce U.S. troops in the Republic of Korea are not true,” calling the alliance “iron clad.” Gen. Brunson had told the Senate Armed Services Committee in April 2025 that a drawdown would be “problematic,” citing the troops’ role in ballistic missile defense.¹⁹

Congress has moved to lock in the current number. Section 1268 of the 2026 National Defense Authorization Act bars using funds to cut USFK below 28,500 unless extensive reporting requirements are met. The Trump administration “strongly opposed” the provision, arguing it infringed on the president’s authority as commander in chief, but it stayed in the final bill.²²

How the Alliance Is Shifting

Wartime Operational Control

A US four-star general leads the Combined Forces Command in wartime under current arrangements. For more than a decade, the two allies have planned to shift that authority to a South Korean commander, with an American general as deputy. Gen. Brunson submitted a roadmap to the Pentagon in April 2026 targeting the second quarter of fiscal year 2029; Seoul has pushed for completion around 2028. A senior South Korean presidential official called the roughly one-year gap “adjustable.”²³

The transfer is conditions-based. The 2027 NDAA requires the Secretary of War to report to Congress every 90 days starting March 2027 on South Korea’s military readiness, allied counter-capabilities against North Korean threats, and the regional security environment. The secretary must also certify at least 60 days before any transfer that it aligns with US national interests. Gen. Brunson has said publicly that “political expediency must not precede conditions.”²⁴

Nuclear Deterrence

Extended nuclear deterrence — the American pledge to defend South Korea with its full range of capabilities, including nuclear weapons — has been a pillar of the alliance since the Cold War. Confidence in that pledge has weakened as North Korea’s arsenal grew. By 2023, polls showed 71 percent of South Koreans supported developing an independent nuclear capability.²⁵

To reinforce the alliance and dissuade Seoul from going nuclear, the Biden administration and South Korean President Yoon Suk-yeol issued the Washington Declaration in April 2023, creating the Nuclear Consultative Group. The group brings senior defense officials together to discuss nuclear strategy, run tabletop exercises with US Strategic Command, and coordinate crisis communications, giving South Korea a level of involvement in nuclear planning previously reserved for NATO allies.²⁶ The declaration also led to more visible deployments of US nuclear-capable assets, including port calls by ballistic missile submarines.²⁵ Even so, public support for an independent South Korean nuclear force reached 76.2 percent in a 2025 Asan Institute survey, and confidence that the US would actually use nuclear weapons to defend South Korea sat at only 48.9 percent.²⁷

Nuclear-Powered Submarines

In October 2025, President Trump agreed to support South Korea’s pursuit of conventionally armed, nuclear-powered attack submarines. A month later the two countries announced a framework for cooperation, with the US committing to consult on ways to source nuclear fuel.²⁸ The “Chang Bogo N Project” aims to put South Korea’s first nuclear attack submarine in the water by the mid-2030s. It will require negotiating “subsequent arrangements” under Section 123 of the Atomic Energy Act, a process that could take years.²⁹ Nonproliferation experts have warned that US support for South Korean uranium enrichment and spent fuel reprocessing could create a latent weapons capability and risk a regional arms race.³⁰

Regional Sustainment Hub

Gen. Brunson has proposed turning South Korea into a Regional Sustainment Hub to maintain, repair, and overhaul US warships, aircraft, and missile systems closer to the theater. South Korean shipyards have already performed depot-level maintenance on US Navy transport ships and on fighter aircraft including F-16s, F-15s, and C-130s.³¹ As of May 2026, Brunson told Congress the hub is “partially operational” and said congressional approval of “special repair authority” is needed to expand the types of platforms South Korean firms can work on.³²

Tour Lengths

Most US Army tours in South Korea have historically been 12-month unaccompanied assignments, which drove high personnel turnover. On October 1, 2025, the Department of Defense began implementing a “3-2-1” model: 36-month accompanied tours, 24-month unaccompanied tours, and 12-month tours only as exceptions when accompanied assignments cannot be supported.³³ Kunsan Air Base and Camp Mujuk are excluded from the new standard due to infrastructure constraints. The policy applies only to new assignments, with full implementation expected by October 2027.³⁴

What South Koreans Think

Despite periodic controversies, the American presence commands broad public support in South Korea. A March 2025 survey by the Asan Institute found that 80.1 percent of South Koreans support the presence of US forces, and 71.2 percent favor the current 28,500 troop level, up 5.8 percentage points from the previous year, a shift attributed to concerns about potential withdrawals under a second Trump term. Some 96 percent consider the alliance necessary for the foreseeable future, and 85.8 percent choose the United States over China if forced to pick — the highest level Asan has recorded.²⁷

A separate May 2026 global poll by Nira Data put South Korea’s net approval for hosting US bases at +14, the second-highest score among all countries with American troops, notable given that 90 of the 97 countries surveyed showed net opposition.³⁵ Support is not unqualified. Roughly half of South Koreans remain pessimistic about the future of the alliance given uncertainty over trade, troop levels, and semiconductor subsidies under the current American administration.²⁷

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