Over the past seven decades, the ROK-U.S. alliance has evolved through considerable change, shaped by shifts in the international environment, the growing North Korean threat, and the foreign policy of successive U.S. administrations. Cooperation continues between the Trump administration and the Lee Jae Myung administration, and the alliance today is moving beyond the military domain into a more comprehensive partnership spanning the economic, technological, and other fields. Even so, the military alliance continues to play a central role, and it faces the serious task of overcoming the advancement of North Korea’s nuclear and missile capabilities alongside intensifying U.S.-China strategic competition.

For the alliance to develop further, sharing common values and threat perceptions matters more than a purely transactional give-and-take. This has, in fact, been a key reason the alliance has remained firm over the past seventy years. Yet pragmatic responses to present circumstances are no less important than this shared normative foundation, since unresolved friction in the near term can obstruct future cooperation. This paper accordingly examines the key current issues facing the alliance, along with each country’s priorities and possible approaches to addressing them.

The joint fact sheet released following last November’s ROK-U.S. summit shows that South Korea agreed, as part of alliance modernization, to raise its defense spending to roughly 3.5 percent of GDP, to purchase approximately 25 billion dollars’ worth of U.S. military equipment, and to provide comprehensive support for U.S. Forces Korea. In exchange, South Korea secured U.S. commitments to an early transfer of wartime operational control and to cooperation on the construction of nuclear-powered submarines and the procurement of fuel for them, a long-standing goal of the South Korean military. The arrangement likewise serves U.S. interests. In exchange for maintaining a stable U.S. troop presence on the peninsula and providing a robust, integrated extended deterrence, the United States secured greater “strategic flexibility,” enabling U.S. Forces Korea to contribute more broadly to the Indo-Pacific beyond the Korean Peninsula.

At the same time, the two countries are also deepening cooperation in mutually beneficial areas, including the development of multi-domain operational capabilities spanning space and cyber, shipbuilding cooperation, and cooperation across the defense industrial supply chain. Because these areas are relatively free of the obligations and entitlements embedded in the broader alliance relationship, they carry little political burden and offer considerable room for advancing the alliance. Military-to-military cooperation between the two countries in these areas should accordingly proceed with urgency.

Going forward, alliance modernization will likely face a range of challenges as the international environment shifts and U.S. administrations’ positions evolve. To meet these challenges, South Korea needs to take a proactive approach, offering increased defense spending, purchases of U.S. weapons systems, and a measure of accommodation for the strategic flexibility of U.S. Forces Korea, while in turn securing its own objectives in a timely manner: strengthened military capability, a stable transfer of wartime operational control, the cultivation of multi-domain operational capability, entry into the U.S. defense market, and the construction of nuclear-powered submarines, the last of which will require persuading the U.S. Congress to amend the relevant legislation.

In the near term, South Korea needs to develop a concrete accounting strategy for the efficient use of its defense budget and expand cooperation on maintenance, repair, and overhaul (MRO) work for U.S. Navy vessels as a pathway into the U.S. defense market, while also establishing concrete success stories in that market. Securing a stable basis for nuclear-powered submarine propulsion will require a framework agreement with the Trump administration, alongside systematic policy implementation on the acquisition of U.S. weapons systems. Over the medium term, South Korea needs to secure the capabilities required for OPCON transfer and complete the associated verification process. On this basis, it should pursue a transfer of OPCON that is both conditions-based and achieved as early as feasible, with a roadmap in place to keep bilateral consultations on track and head off unnecessary friction. At the same time, South Korea needs to secure U.S. congressional support for its nuclear-powered submarine program and pass the exception to the atomic energy agreement that this would require, while also completing the Reciprocal Defense Procurement (RDP-A) agreement to lay the groundwork for more active cooperation across the defense industrial supply chain.

Over the longer term, looking five years and beyond, the alliance needs to institutionalize a system capable of conducting multi-domain operations. This will require South Korea to substantially expand its own capacity to jointly conduct operations not only across land, sea, and air, but in space and cyberspace as well.

The ROK-U.S. alliance has, over more than seventy years, been regarded as one of the most successful alliances in the world, yet differences in strategic priorities and national interests between the two countries have given rise to sources of friction in the military and security domain, some latent and others already apparent. The first concerns a clash between global strategic priorities and regional security priorities. The United States seeks to employ its forces in Asia, including U.S. Forces Korea, with greater flexibility in order to counter China across the Indo-Pacific. South Korea’s position, by contrast, is that the primary mission of U.S. Forces Korea remains deterring North Korean provocations and preparing for a full-scale North Korean attack. Managing this tension is important, and cooperation should proceed along lines in which the United States is granted a measure of flexibility while maintaining strategic ambiguity, and South Korea’s forces continue to focus primarily on deterring North Korea on the peninsula.

The second concerns the timing and conditions for OPCON transfer. A subtle difference in emphasis persists between South Korea’s push for an early transfer of OPCON to the South Korean military and the U.S. position that the South Korean military’s capacity to lead must be rigorously verified. Even as the government pursues an early transfer, it must do so in parallel with efforts to meet the verification criteria for the Future Combined Forces Command’s capabilities. In this process, unnecessary disputes must not be allowed to weaken the combined defense posture. Accelerating the timeline will require a corresponding level of investment, not only in the hardware of weapons systems but, more importantly, in enhancing the operational expertise of South Korea’s armed forces. It is worth noting that pursuing this investment alongside an earlier transfer timeline is what will sustain trust between the two countries’ military authorities and ensure that the U.S. contribution to South Korea’s security in a contingency does not diminish.

The third concerns the need to make extended deterrence more concrete and substantive. Absent persistent South Korean engagement on this front, the United States may be content with a merely adequate level of extended deterrence cooperation. Given the advancing North Korean nuclear threat it faces, however, South Korea’s position must be different. To sustain the credibility of U.S. extended deterrence, the two countries need to concretely institutionalize a system of joint nuclear planning and execution through the Nuclear Consultative Group (NCG). Operational-level cooperation on extended deterrence between the two countries needs to be completed, encompassing both the timing of U.S. strategic asset deployment to the Korean Peninsula in the event of a North Korean nuclear threat and the “nuclear options” South Korea would be able to request. Building on this foundation, the two countries should advance Conventional-Nuclear Integration (CNI) exercises that combine South Korea’s advanced conventional forces with U.S. nuclear forces, in order to further consolidate mutual trust.

It bears emphasizing that resolving these sources of friction between South Korea and the United States should not come at the cost of one-sided concessions by either side. In building mutual trust, the two countries should work to establish reciprocal practices rather than demanding sacrifice from one party alone. This will require responding constructively to the transactional approach to alliance modernization taken by the Trump administration, while at the same time exercising the wisdom to persuade the United States and to resolve, without unnecessary delay, the tasks that must be accomplished over the medium to long term.​