The unusual convergence between Seoul and Washington toward greater South Korean defense autonomy could reshape the purpose of the US military presence on the Korean Peninsula. The implications of this convergence could strengthen or complicate US-led allied deterrence in the event of a Taiwan contingency.
For Taipei, the key question is whether Seoul and Washington agree on what US forces on the peninsula are for and whether they should be available for contingencies beyond South Korea. Even if US forces there did not directly participate in a Taiwan contingency, their role within the broader US logistical and support architecture across the Western Pacific makes it impossible to divorce the peninsula from such a conflict.
Despite the very different political outlooks of US President Donald Trump and South Korean President Lee Jae-myung, last week’s decision announcement reducing the annual joint US-Republic of Korea (ROK) Ulchi Freedom Shield (UFS) exercise coincides with a longstanding push by some in Seoul to transfer wartime operational control (OPCON) within the US-ROK Combined Forces Command (CFC) from a US Army four-star general to an ROK Army counterpart.
For some South Koreans, especially in Lee’s progressive coalition, OPCON transfer represents more than a technical reorganization of the CFC. It raises the broader question of how Seoul and Washington should divide responsibility for defending the peninsula.
Yet, greater ROK responsibility for deterring North Korea raises an uncomfortable question that directly affects Taipei and regional allies: If Seoul assumes greater responsibility for its own defense, what purpose should the 28,500 US troops stationed on the peninsula serve? Washington’s emerging answer is greater strategic flexibility for US forces on the peninsula.
The diminished emphasis on North Korea as a direct threat to the US homeland in the recent US National Security and National Defense Strategies, alongside the growing use of US forces on the peninsula for unilateral and third-country exercises, reflects the push for greater “strategic flexibility” that CFC commander General Xavier Brunson has repeatedly emphasized.
US Undersecretary of Defense for Policy Elbridge Colby reinforced this logic in Manila last week, arguing that stronger allies should assume greater responsibility for their own defense as Washington builds a more resilient regional deterrence architecture.
However, Seoul has its own interests. Greater South Korean defense autonomy does not necessarily imply greater willingness to allow US forces stationed on the peninsula to be employed against China in a regional contingency.
The US military presence on the peninsula remains rooted in the unfinished Korean War and the alliance’s mission of deterring North Korean aggression. Washington’s push for greater “strategic flexibility” must therefore contend with the political constraints governing how those forces can be employed beyond Korea, a reality that directly affects Taiwan’s security.
Paradoxically, the harder Washington pushes Seoul to assume greater responsibility for its defense to increase US strategic flexibility, the more it could strengthen South Korean demands for autonomy that constrain Washington’s ability to employ peninsula-based forces in regional contingencies.
OPCON transfer also carries questions of sovereignty and strategic agency alongside warfighting effectiveness. Wariness of strategic flexibility in the alliance was reflected in the 2006 joint US-ROK statement that launched the Strategic Consultation for Allied Partnership. The statement, issued at the height of the Global War on Terror, recognized the need for flexibility for peninsula-based US forces while affirming that South Korea should not be drawn into a regional conflict “against the will of the Korean people.”
OPCON transfer was also a priority for Lee’s predecessor, Moon Jae-in. Still, it remained incomplete when he left office, as COVID-era reductions in combined exercises delayed crucial capability assessments. Ironically, reducing the UFS exercise could once again complicate the capability assessments necessary to advance Lee’s push for OPCON transfer.
A Taiwan contingency could bring this paradox to a head. Washington would likely seek greater flexibility from its South Korea-based forces precisely when Seoul, fearing North Korean opportunism amid a wider regional conflict, wants more US capabilities focused on the peninsula.
Taipei therefore has an enormous stake in how Seoul’s pursuit of greater defense autonomy reshapes the US-ROK alliance. OPCON transfer could make South Korea more capable while simultaneously opening a new political argument over what South Korea-based US forces are actually for.
For Taiwan, the larger lesson extends beyond the peninsula. Assessing the US’ ability to respond to a Taiwan contingency requires more than counting US forces in the Indo-Pacific region. Taipei must also understand the alliance politics governing how those forces can be used. Developments in Seoul — and in other allied capitals — could ultimately shape what Washington is politically and militarily able to do in a crisis.
Bryce C. Barros is a visiting fellow at the Institute for National Defense and Security Studies. He served as a US Senate National Security Advisor from 2023 to 2024. The views expressed here do not reflect those of the US government or other affiliations.
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