The evolving role of U.S. forces in Korea

By Jihoon Yu 
Real Clear Wire

The presence of U.S. Forces in Korea (USFK) has long served as a cornerstone of the Republic of Korea–United States (ROK-U.S.) alliance, functioning as both a deterrent against North Korean aggression and a symbol of the U.S. commitment to security on the Korean Peninsula. However, amid intensifying strategic competition in the Indo-Pacific and shifting priorities within Washington, the traditional role of USFK is being redefined. This evolution carries profound implications—not only for the future structure of the alliance, but also for deterrence, regional stability, and South Korea’s own defense posture.

Historically, the rationale for maintaining approximately 28,500 U.S. troops in South Korea has centered on deterring the North Korean threat. The Demilitarized Zone remains one of the most heavily fortified borders in the world, and Pyongyang’s continued development of nuclear and missile capabilities reinforces the enduring logic of forward-deployed deterrence. Yet U.S. strategic thinking is increasingly framing the Korean Peninsula as a strategic forward base—an “unsinkable aircraft carrier”—for broader power projection across the Indo-Pacific.

This expanded perspective was recently underscored by General Xavier Brunson, commander of USFK, who stated that U.S. forces in Korea serve not only to deter North Korea, but also to address wider regional challenges, including countering China’s growing military assertiveness and preparing for potential regional contingencies such as a Taiwan Strait conflict. These statements align with the U.S. military’s global posture review and its emphasis on integrated deterrence—an approach shaped by the recognition that U.S. forces must deter and, if necessary, respond to threats posed by multiple state actors in overlapping theaters.

Redefining USFK’s mission may enhance the alliance’s relevance in a region where multilateral deterrence is becoming increasingly necessary. At the same time, it risks blurring the clarity of the U.S. security commitment to South Korea, particularly if Seoul perceives that its defense is being subsumed under broader regional objectives. This concern is not unfounded. During the previous U.S. administration, calls for significant increases in South Korea’s burden-sharing contributions and suggestions of troop withdrawals triggered a debate in Seoul over the credibility and stability of the alliance. These issues have resurfaced amid speculation that a future U.S. administration might prioritize Taiwan-related contingencies at the expense of longstanding commitments on the peninsula.

For South Korea, this evolving U.S. posture introduces a layer of strategic uncertainty. While the intention in Washington may be to increase flexibility and deterrence across the region, there is growing concern in Seoul that the alliance could be shifting toward a more transactional arrangement, especially under renewed “America First” thinking. A widening gap in strategic priorities—China for Washington, North Korea for Seoul—could erode alliance cohesion if not carefully managed. This divergence has already begun to spark internal debates within South Korea about the need for greater defense autonomy, including reconsideration of nuclear options—an issue gaining traction among segments of the public and political elite.

Operationally, the dual-hatted role of USFK—deter North Korea while contributing to regional contingencies—places significant demands on interoperability, flexible command-and-control structures, and readiness. It requires a recalibration of joint operational planning, with clear answers on how U.S. assets would be prioritized in the event of simultaneous crises, one on the Korean Peninsula and another in the Taiwan Strait or South China Sea. This shift also reinforces the need for South Korea to accelerate its defense modernization efforts. Investments in missile defense, space-based surveillance, ISR capabilities, and indigenous strategic strike assets reflect Seoul’s growing recognition that its security must not be overly dependent on U.S. forces alone.

In this context, the future of the alliance depends heavily on political alignment and shared strategic understanding. Initiatives such as the trilateral cooperation framework among South Korea, the U.S., and Japan, advanced during the Camp David summit in 2023, represent meaningful progress toward integrated regional deterrence. However, overcoming historical mistrust—especially between Seoul and Tokyo—and aligning priorities across three capitals remains a difficult, yet essential, task.

The evolving role of USFK presents a double-edged sword. It could strengthen the alliance if used as a platform to promote broader regional cooperation, conduct multilateral exercises, and integrate allied capabilities. But it could also strain the alliance if South Korea perceives that its unique security concerns are being overshadowed by Washington’s broader regional agenda or if U.S. political leaders treat the alliance as a bargaining chip in unrelated negotiations.

To ensure long-term credibility and resilience, both governments must engage in transparent and sustained dialogue on the changing mission of USFK and the broader strategic goals of the alliance. Mutual commitments must be reaffirmed, burden-sharing frameworks should be institutionalized in a way that enhances collective capabilities rather than transactional arrangements, and the Combined Forces Command structure should be updated to meet emerging operational demands.

At the same time, the U.S. must be cautious not to conflate its Indo-Pacific strategy with its specific obligations under the ROK-U.S. alliance. The strategic value of U.S. forces in Korea lies not only in their geographic location, but also in their credibility as a deterrent against North Korean aggression and their symbolic role in maintaining alliance solidarity.

Ultimately, the redefinition of the U.S. military presence in Korea reflects broader shifts in the global security environment and the need to deter multiple threats across a contested Indo-Pacific. While this transformation offers opportunities to reinforce regional stability through flexible military posturing and integrated deterrence, it also introduces real risks of misalignment and erosion of trust. To navigate this complex environment, the ROK and U.S. must clarify strategic roles, update planning assumptions, and adapt their alliance not only to evolving external threats, but also to the internal political dynamics that shape public confidence and national decision-making. Only with such a deliberate, forward-looking approach can the ROK-U.S. alliance sustain its strategic edge in a rapidly changing world.

Jihoon Yu is a research fellow and the director of external cooperation at the Korea Institute for Defense Analyses. Jihoon was the member of Task Force for South Korea’s light aircraft carrier project and Jangbogo-III submarine project. He is the main author of the ROK Navy’s Navy Vision 2045. His area of expertise includes the ROK-US alliance, the ROK-Europe security cooperation, inter-Korean relations, national security, maritime security, and maritime strategy. He earned his MA in National Security Affairs from the US Naval Postgraduate School and PhD in Political Science from Syracuse University.