With the drawdown of U.S. forces in Germany underway, a reduction of U.S. forces in South Korea is now more likely than ever, given evolving U.S. defense priorities and longstanding trends on the Korean Peninsula. Rumors of an imminent U.S. force drawdown in Korea have been circulating since at least 2019, and President Donald Trump has made it clear he wants to reduce large overseas basing. South Korea, however, is a particularly contentious case, as any changes to the size and structure of U.S. forces must take into consideration both the local mission of deterring against North Korea, as well as the broader U.S. strategic mission of refocusing on great power competition, particularly with China. And that will require reassessing South Korea's own national defense capabilities, the benefits and risks of having a large forward force based on the Asian mainland, and the impact of any shift in forces on the overall perception of U.S. commitment and reliability with other allies and partners in the region.
The Question of U.S. Forces in South Korea
Since the end of the Cold War, the United States has sought to reduce its large-scale overseas basing, both to reduce financial and political costs and create a more flexible and responsive force structure better adapted to the changing threat dynamic. Cost-sharing agreements are often contentious, and the current stalemate between the United States and South Korea has dragged on with no end in sight. U.S. basing is also often a source of protest inside South Korea, over land use, accidents or illegal behavior by U.S. personnel, and the perception of continued occupation. Reducing the U.S. footprint and shifting more to naval, air and rotational units could ease these tensions.
Under the current National Defense Strategy (NDS), Secretary of Defense Mark Esper is now reviewing the overall posture of U.S. forces abroad, with the mandate toward a more flexible forward posture. Since the early 2000s, U.S. forces in Korea have moved out of the major facility at Yongsan in Seoul. The United States has also pulled most of its forces south of the Han River. During the Iraq War, the administration of U.S. President George W. Bush cut total troop numbers in Korea by nearly 12,000 as well, in part because forces based in Korea cannot be readily used for contingencies elsewhere.
Amid reports that the Pentagon had already recommended force restructuring in Korea, Esper said on July 21 that he had given no order to withdraw forces, but then emphasized that he was reviewing all geographic combatant commands in line with the current NDS, with a desire for more rotational forces and greater strategic flexibility.
In that context, a longstanding suggestion for reshaping the U.S. military posture in South Korea is a further shift toward more naval and air assets, and reduced U.S. ground forces — potentially moving more ground forces to a rotational basis, rather than extended deployments. Doing so would maintain a deterrent presence in Korea and retain the benefit of training with South Korean forces, while still reducing constraints due to limits on the deployment of Korean-based forces to conflicts elsewhere. Rotational forces also have a smaller footprint in overseas basing, as they do not include family or family support functions that extended deployments entail.
The restructuring of U.S. forces, however, is complicated by U.S. operational control (OPCON) over South Korean forces in the event of war. South Korea has had its military under U.S. OPCON since the Korean War in the early 1950s, with the South Korean military only regaining formal OPCON of its own forces in peacetime in 1994. Over the decades, the transfer of wartime OPCON to South Korea has been delayed numerous times due to its military's perceived unreadiness and occasional flare-ups of tensions with North Korea. For South Korea, particularly under liberal governments like that of current President Moon Jae In, OPCON transfer is a critical step to fully realizing its independence and national pride. Korea was under Japanese control from 1910 to 1945, and has had its military under U.S. OPCON since the Korean War. And while its alliance with the United States remains important for Seoul, the nature of the two countries' military relationship is still at times seen as paternalistic
The Case for Restructuring
There are several arguments in support of such a restructuring. For one, U.S. forces in South Korea are largely a Cold War left-over and are limited in use for operations outside the country. South Korea, Germany and Japan continue to represent the largest hosting of U.S. forces abroad, and the largest expenditures for basing. Prior to the announced drawdown, Germany hosted more than 35,000 U.S. forces, South Korea more than 26,000 and Japan more than 55,000, according to the latest tally by the Heritage Foundation's Defense Manpower Data Center. The Pentagon has traditionally avoided using U.S. forces stationed in South Korea for operations elsewhere, both due to the North Korean threat and to South Korean political concerns.
The balance of forces on the Korean Peninsula also currently favors South Korea, reducing the necessity of a large ready U.S. presence. That balance was an important consideration in U.S. President Richard Nixon's decision to reduce forces in South Korea in 1971, desiring for Seoul to carry more of the burden for its own national defense. A revision of U.S. intelligence estimates of North Korean strength also played a role in reversing President Jimmy Carter's decision to further reduce forces in South Korea less than a decade later.
North Korean capabilities no longer require the U.S. force posture currently configured in South Korea as well. While North Korea has significantly improved its missile and rocket capabilities, the effective counter is not necessarily more forces open the ground, but rather improved missile defense capabilities and the development of South Korean counter-strike capabilities. South Korea has been constrained in the latter for decades by the United States for fear of triggering a war with North Korea that would lock Washington into conflict. But Washington recently agreed to allow Seoul to develop solid-fuel rockets and has expanded its acceptable payload size. South Korea has also recently identified ground and air-launch missiles as a key component of its force development, along with local missile defense. Given the developments in the South Korean military and the situation in North Korea, it is unlikely that Pyongyang would see a reduction of U.S forces in South Korea as an invitation to roll tanks south.
But there are also valid arguments against a U.S. withdrawal from South Korea, including:
Preserving a key, amphibious entry point to Asia in the case of a U.S.-China conflict. South Korea's most concrete value to the U.S. defense posture is perhaps its role as an amphibious bridge between the maritime world and the Asian continent. Strategic competition between the United States and China plays out where the maritime power of the United States meets the continental power of China. Korea has long been the bridge between maritime Japan and continental China, for culture as well as warfare — serving as the launching point for the Mongol invasions of Japan in the 13th century, the Japanese attempted invasion of China in the 16th century, and the Japanese imperial invasion of Asia in the late 19th and early 20th century. The United States is strengthening military ties with other amphibious points around the Chinese periphery, including Vietnam and India. And while South Korea may be vulnerable due to its lack of strategic depth, its proximity to the Chinese north fleet and Beijing also makes it a key strategic point.
Maintaining the longstanding U.S.-South Korea relationship. In both South Korea and the United States, support of a continued robust U.S. force presence is often based on the two countries' 70-year military partnership. U.S. forces fought in Korea, Korean forces fought alongside the United States in Vietnam, and the two continue to train together.
Reassuring other allies of the United States' commitment to the region. A robust presence of U.S. forces in South Korea also serves as a consistent reminder to North Korea, and perhaps China, of a U.S. commitment to protect its democratic allies in the region. Since the end of the Cold War, North Korea clearly took this to heart, and its military development has shifted from a focus on overwhelming the South Korean ground forces to a missile, rocket and cyber-heavy emphasis that targets the U.S. forces and interests. Countering these capabilities requires a nearby U.S. presence, just as countering Russian threats or Iran's missile and nuclear developments require U.S. military operations across Europe and the Middle East, respectively.
A reduction of forces could signal that, despite its Pacific Defense Initiative, the United States is more concerned with keeping competition and conflict bottled up in Asian waters far from U.S. shores, rather than strengthening and defending its allies and partners. Despite hosting more U.S. troops, Japan is particularly sensitive to any changes to the presence of U.S. forces in South Korea, which helps buffer it from Asian conflict. Japan has been very vocal each time a major revision to U.S. forces in South Korea has been contemplated, as a complete withdrawal would leave Japan the frontline. And while Tokyo has gone far to reinterpret its pacifist constitution, there is still strong political and social sentiment against Japan's role as a regional belligerent.