Three Major Issues and Tasks of the ROK-U.S. Alliance: Increase in Defense Cost-Sharing, Adjustment of U.S. Forces in Korea, and Transfer of Wartime Operational Control​

Jungsup Kim

jungsupkim@sejong.org​

Principal Research Fellow

Sejong Institute

1. Problem Statement

Following the inauguration of the second Trump administration, which advances an “America First” agenda, and amid ongoing changes in the war in Ukraine and NATO policies, the prospect of a fundamental upheaval within the ROK-U.S. alliance is becoming apparent. Economically, tariffs are the foremost concern, but in terms of security, the issues of defense costs, U.S. Forces Korea (USFK), and the transfer of wartime operational control (OPCON) are expected to become the three most important agenda items. First, the standard of 5% of GDP applied to NATO defense expenditures appears likely to be demanded of South Korea in a similar manner, and beyond that, cost pressures such as increases in defense cost-sharing and the transfer of expenses for the deployment of strategic assets may become more overt. Second, reports have emerged that reductions of USFK are under consideration, and the issue of strategic flexibility — namely, the potential use of USFK in regional contingencies — has also been highlighted through statements by the Indo-Pacific Commander and the USFK Commander. Third, if there is an overall adjustment of U.S. military posture in the Indo-Pacific region, there is also the possibility of significant changes in the U.S. Forces Japan, the United Nations Command, and the ROK-U.S. Combined Forces Command. In particular, in this case, the issue of OPCON transfer is also expected to be emphasized. This paper seeks to present measures for consultations with the United States on each of the three major agenda through analysis, and it is expected that this will also be of help for comprehensive judgment in the event of a broader give-and-take review in the future. In particular, since the above alliance issues originate in changes in U.S. strategy, it is desirable to approach them not passively or defensively, but actively and forward-looking, from the perspective of a ROK-led transformation of the alliance.

2. Cost Pressure and Burden-Sharing: Increase in Defense Spending and Cost Sharing

1) Trends in Cost Pressures under the Trump Administration

Following in his victory in the presidential election, President Trump has demanded that NATO member states increase defense spending to 5 percent of GDP, and he ultimately secured this at the NATO Summit in June 2025. Subsequently, the United States, having extracted commitments for increased defense spending from NATO, has indicated that similar standards may be applied to Asian allies such as South Korea and Japan. Secretary of Defense Pete Hegseth mentioned at the June 18 hearing of the Senate Committee on Armed Services that a new standard for defense spending has been established for allies worldwide, including in Asia. Meanwhile, apart from the requirement for defense spending standards, there also exists the possibility that an increase in the defense cost-sharing contribution for U.S. Forces Korea, as well as contributions toward the U.S. security commitment on the Korean Peninsula, may be demanded. President Trump has strongly pressed for increased defense cost-sharing from South Korea since his first administration, and during the 2024 presidential campaign, he referred to South Korea as a “money machine,” asserting that if he were president, South Korea would pay $10 billion annually. This amounts to roughly nine times the current level agreed under the 12th Special Measures Agreement (SMA).

2) Response to Increasing Defense Spending to 5% of GDP

It is virtually impossible to raise South Korea’s defense budget to 5% of GDP at face value. In 2024, South Korea’s defense spending as a share of GDP is 2.33%. To increase it to 5% of GDP, an additional 68.31 trillion won (KRW) would need to be invested, which is approximately 114% of the current defense budget. Defense spending accounts for about 9.1% of the total government budget, and if it were increased to 5% of GDP, the share of defense spending in total government finances would have to rise to 19.4%, more than doubling. In theory, the share of defense spending could be raised through government will and prioritization adjustments, but given the government budget structure, roughly 50% of total expenditure is rigid spending, making such bold adjustments practically impossible. The only option would be to abandon balanced budgeting and secure funds for defense spending increases through government bond issuance; however, to meet the 5% of GDP standard, permanent borrowing would be required, which would place a significant burden on national fiscal soundness.

Applying the 5% standard used for NATO uniformly to South Korea and other Asian allies is inappropriate in light of the nature of the threats and the level of burden-sharing within the alliance. The criticism that NATO member states in Europe have been free-riding on the U.S. security umbrella was not newly raised by the Trump administration; it has been a persistent alliance issue discussed since the post-Cold War period. Therefore, although Trump’s 5% standard had a somewhat coercive character, the agreement reached at the recent NATO summit was not simply a result of yielding to U.S. pressure, but also reflected Europe’s own geopolitical awakening as an important background factor. In contrast, South Korea is a typical security state that has maintained an elite standing army of 500,000 personnel and has spent a high level of defense expenditure—around 10% relative to government finances—to prepare for the existing North Korean threat. South Korea’s defense spending as a share of GDP, at 2.33%, is the highest among Asian allies. In particular, in terms of conventional military power, it is generally assessed that South Korea already surpasses North Korea through continuous investment. Raising defense spending to 5% would only represent additional reinforcement in an already superior conventional area. Of course, there are areas where the Republic of Korea Armed Forces still need to reinforce and develop conventional capabilities, but this differs from Europe, where comprehensive rearmament and the expansion of the defense industry base are required.

Despite practical difficulties and logical inappropriateness, if the Trump administration demands the 5% standard from South Korea, simply rejecting it will be difficult, so realistic measures such as adjusting the method of calculating defense spending need to be prepared. First, as NATO did, it would be possible to seek recognition of investment in broad security costs by including, in addition to pure defense spending, the promotion of the defense industry, national research and development (R&D), and veterans’ budgets. Furthermore, as with NATO’s agreement, the process of achieving the defense spending target would take place over more than ten years, making it possible, for the time being, to buy time while striving to maintain U.S. security engagement. However, the straightforward approach is not about formal defense spending targets, but an approach that expresses the intention to strengthen South Korea’s defense capabilities based on genuine requirements that can be agreed upon with the United States. In other words, at least regarding conventional threats, South Korea will bear the primary responsibility, and the U.S. burden will decrease. Setting priorities for government spending is a natural right and duty of a sovereign state. Even though it is a request from an ally, it is necessary to make efforts during the negotiation process to secure maximum fiscal autonomy by raising the specific characteristics of security on the Korean Peninsula.

3) Response to Pressure on Defense Cost-Sharing

If there is a demand from the U.S. to increase the defense cost-sharing contribution, it is necessary, first, to maintain the basic position that the 12th SMA, agreed upon by both South Korea and the United States, must be observed. The 12th SMA was agreed upon by the South Korean and U.S. authorities only one year and eight months ago and is an intergovernmental commitment that regulates contributions for five years, until 2030. Some argue that the renegotiation of the defense cost-sharing contribution should be taken as a given and that Trump’s demands should be proactively accepted. However, yielding to U.S. demands early is neither consistent with South Korea’s national dignity nor advantageous in terms of negotiation strategy. Nevertheless, if renegotiation of the SMA becomes unavoidable, it is necessary to curb a sudden increase in the defense cost-sharing contribution through changes in the calculation method. Specifically, it is worth considering proceeding with negotiations by shifting the method of calculating contributions from the current “total amount-based” approach to a “requirements-based” approach. While South Korea has so far considered the total amount-based method advantageous, in order to respond to Trump’s indiscriminate pressure and restrain a rapid rise in contributions, the requirements-based method has become more favorable.

In addition, preparation is needed for the possibility that the U.S. may demand new cost-sharing outside the framework of the SMA. As Acting Ambassador Joseph Yun indicated, the Trump administration could request that South Korea bear the costs of strategic asset deployments (strategic bomber flights, carrier strike group dispatches, etc.) and ROK-U.S. joint exercises (Key Resolve/Foal Eagle exercises, UFG, etc.), which are not included in existing SMA items. In fact, during the 11th SMA negotiations conducted under the first Trump administration in 2019, the U.S. side requested the establishment of a new item called “operational support.” Regarding such new demands outside the SMA framework, it is necessary to emphasize that they should be handled in accordance with the spirit of the alliance, while approaching negotiations with a stance that does not exclude forward-looking reviews for cost reduction in high-cost alliance operations. Excessively frequent strategic asset deployments and large-scale joint exercises are not necessarily militarily effective for deterrence against North Korea and can have negative effects on the strategic stability of the Korean Peninsula. Strategic asset deployment is an important means to ensure the credibility of extended deterrence, as it reassures the ally (South Korea) while simultaneously inducing fear in the adversary (North Korea). The problem is that if such deployments are too frequent or excessive, the deterrence and assurance effects can be diminished (similar to the principle of diminishing utility), creating a future burden to operate in a more provocative and offensive manner. Therefore, if the anticipated strategic effects are difficult to achieve, coordination between South Korea and the U.S. will be required for these high-cost alliance operations, considering economic aspects as well. While an appropriate level of exercises and strategic asset deployments is necessary, it is desirable to comprehensively consider overall costs and deterrence effects.

3. Adjustment of U.S. Forces in Korea: Changes in Size, Role, and Character

1) Trends Regarding the Reduction of U.S. Forces Korea and Strategic Flexibility

On May 25, the Wall Street Journal (WSJ) reported that the U.S. Department of Defense is considering a plan to relocate approximately 4,500 of the 28,500 U.S. Forces Korea personnel to Guam and other locations within the Indo-Pacific region. The discussion of reducing USFK is part of a strategic realignment aimed at shifting the U.S. military focus in the Indo-Pacific region toward containing and responding to China. In addition, the reduction of overseas-deployed U.S. forces is also related to the Trump administration’s policy of reducing the fiscal deficit under the pressure of an unsustainable national debt and the resulting interest costs.

Meanwhile, the issue of “strategic flexibility” has also emerged, emphasizing that U.S. Forces Korea should not function as a fixed force solely for responding to the North Korean threat but should be utilized flexibly in regional military contingencies. Elbridge Colby, Under Secretary of Defense for Policy, who is reportedly leading the drafting of the Trump administration’s National Defense Strategy (to be published in August 2025), is a figure who holds the belief that “U.S. Forces Korea should not be constrained by North Korea, and the United States’ main strategic focus should be more on deterring China.” The strategic flexibility of overseas-deployed U.S. forces has been part of the U.S. military strategy pursued since the September 11, 2001 terrorist attacks and was highlighted as an alliance issue during the Bush–Roh Moo-hyun administrations. At that time, the Roh government attempted to secure South Korea’s control over the deployment of U.S. forces outside the Korean Peninsula by stipulating conditions and procedures for extraterritorial deployment of USFK. However, as agreement on specific conditions and procedures regarding the strategic flexibility of USFK proved difficult, the ROK and U.S. governments ultimately announced a compromise outcome that recognized both sides’ needs and concerns.

2) Adjustment and Change in the Character of U.S. Forces Korea

The reduction of U.S. Forces Korea is significant not only in scale but also in terms of which specific units and forces are affected. It is expected that partial reductions of ground forces and adjustments of air force units and capabilities will be possible. Among the units most likely to be affected by a USFK reduction is the rotationally deployed Stryker Brigade. Within the Seventh Air Force, 24 A-10 attack aircraft stationed at Osan Air Base are scheduled to be retired sequentially. Additionally, the existing fourth-generation F-16 fighter aircraft of the Seventh Air Force are being concentrated at Osan Air Base, while F-35A aircraft are being considered for deployment at Kunsan Air Base. In July 2024, the Seventh Air Force relocated nine F-16s from Kunsan Air Base to Osan Air Base, creating a Super Squadron consisting of 31 F-16s. In October 2025, the remaining F-16s are planned to be moved to Osan Air Base to establish a second Super Squadron. As a result, Osan will host two Super Squadron (each with 31 F-16s, totaling 62 F-16s), while no fighter aircraft will remain at Kunsan Air Base, where the potential deployment of an F-35A fighter wing is being considered.

Meanwhile, a radical proposal has recently been raised by figures close to the current Trump administration, suggesting that the size of U.S. Forces Korea be drastically reduced from the current approximately 28,000 personnel to around 10,000. Dan Caldwell, former senior adviser to Defense Secretary Pete Hegseth, and Jennifer Kavanagh, senior fellow at the think tank “Defense Priority,” argued in a joint report on July 9 for a comprehensive readjustment of the global U.S. military posture to align with U.S. national interests.Regarding the Korean Peninsula, the authors identified all ground combat units not related to base defense—including rotationally deployed combat brigades and most of the two infantry divisions, as well as the Army combat aviation brigades—along with two fighter wings, maintenance, and other support personnel, as targets for withdrawal.

3) Self-Strengthening Initiatives and Management of Entanglement Risks of ROK Armed Forces

The reduction of USFK and the issue of strategic flexibility need to be acknowledged as possible realities and prepared for, considering the overarching strategic changes of the United States in the Trump era. During the first Trump administration, discussions of USFK reductions were largely raised as a means of pressuring South Korea to increase defense cost-sharing; however, current circumstances indicate that adjustments to the posture of U.S. forces in the Indo-Pacific, including USFK, are being pursued as important objectives in themselves. Therefore, attempts to prevent U.S. force reductions through increases in cost-sharing are likely to have limitations. Additionally, some argue that South Korea should contribute to the containment of China to demonstrate the alliance’s strategic value to the United States, but this carries risks of entanglement and potential deterioration in South Korea–China relations, which require consideration from the perspective of South Korea’s overall national interest.

The primary role of USFK lies not in its own combat power, but in its function as a tripwire derived from its presence. As long as a certain level of U.S. forces remains on the Korean Peninsula, the deterrent effect against a full-scale North Korean provocation continues. Therefore, rather than responding overly sensitively to the number of U.S. forces in Korea, it is desirable to emphasize the strength of the ROK-U.S. alliance while accelerating South Korea’s self-strengthening efforts, including compensating for gaps in capability resulting from any reductions.　If the 2nd Infantry Division’s Stryker Brigade and Artillery Brigade are reduced, the South Korean military can bolster its maneuver and firepower capabilities. In particular, air power and missile capabilities that can strike North Korea’s key targets should be strengthened to secure deterrence against both conventional war and North Korea’s WMD threats. In addition, intelligence assets such as satellites and high-altitude UAVs, which have been highly dependent on the United States, should continue to be reinforced, and investments in technology and research and development for future warfare capabilities, including drones and counter-drone electronic systems, should be vigorously pursued.

Regarding the strategic flexibility of U.S. Forces Korea, it is necessary to seek appropriate compromise measures if there is a request from the United States. Strategic flexibility is a core concept in the operation of U.S. forces stationed abroad, and attempts either to deny it or for the South Korean government to exercise full control are unlikely to succeed and could cause significant fractures in the alliance. On the other hand, it should be noted that if strategic flexibility is fully permitted, U.S. forces stationed to prevent war on the Korean Peninsula could paradoxically involve South Korea in a larger war. Therefore, while adhering to the principle that the fundamental purpose and role of the ROK-U.S. alliance lies in the peace and stability of the Korean Peninsula, it is necessary to consider measures to minimize the risk of entanglement in contingencies.

One standard is to allow one-time, out-of-area deployments in a limited manner as long as they do not undermine deterrence against North Korea, but to oppose repeated use of the Korean Peninsula as a launch base. If U.S. combat aircraft take off and land at Osan and Kunsan bases, meaning they launch from the Korean Peninsula, conduct operations over the Taiwan Strait, and return to the Korean Peninsula, this implies that the Peninsula is being used as a launch base to attack Chinese forces, making it difficult to avoid the risk of entanglement. In contrast, if some U.S. air assets stationed in Korea are temporarily deployed to locations such as Okinawa for operations over the Taiwan Strait, it is possible to significantly reduce South Korea’s risk of entanglement. For the United States as well, operating F-16s from Osan within a limited operational radius is less advantageous than conducting operations centered on Okinawa in terms of refueling, logistics, and flight safety. In consultations with the United States, it is necessary to emphasize that maintaining stability on the Korean Peninsula by deterring North Korean provocations remains important in a Taiwan contingency and to persuade them of the Korea-centered nature of USFK and the ROK-U.S. alliance.

4. Adjustment of U.S. Force Posture in the Indo-Pacific and the Transfer of Wartime Operational Control

1) Adjustment of Military Posture in the Indo-Pacific and the Reorganization of the Unified Combatant Command

In line with its strategic orientation focused on countering China, the United States is reviewing a broad adjustment of its force posture in the Indo-Pacific region. If this materializes, a significant change to the ROK-U.S. Combined Defense System would be unavoidable. In particular, the status and role of the U.S. Forces Japan (USFJ) Command may be revised, which would inevitably influence the coordination and reorganization of the United Nations Command (UNC) and the ROK-U.S. Combined Forces Command (CFC), and is highly likely to be linked to discussions on the transfer of Operational Control (OPCON). Over the past several years, the United States and Japan have actively discussed the establishment of a Joint Operations Command (JOC) and a Unified Combatant Command (UCC) to enhance alliance integration and ensure smooth conduct of combined operations. In March 2025, Japan established a JOC to strengthen the integrated operation of the Self-Defense Forces (SDF), and on the U.S. side, parallel discussions have been under way to restructure the USFJ Command into a UCC. Under Washington’s strategic emphasis on deterring China, the strategic value of U.S. forces stationed in Japan has increased, and in this context, there exists a possibility of reorganizing the U.S. regional unified command. Specifically, this would involve upgrading the USFJ Commander from a three-star to a four-star general and concurrently assigning the position of UNC Commander, while at the same time, there remains a possibility that the USFK Commander could be downgraded to a three-star rank.

If the U.S. force posture in the region is adjusted in this direction, concerns may arise regarding the hierarchical ordering of alliances in the Indo-Pacific and the potential subordination of USFK. The reduction of U.S. troop levels on the Korean Peninsula, the downgrading of the commander’s rank, and the early transfer of OPCON could all be interpreted as weakening Washington’s defense commitment to the Korean Peninsula. Moreover, the relocation of the UNC, which is tasked with maintaining the Armistice regime and providing forces in contingencies, to Japan under the dual-hatted authority of the USFJ Commander would represent an uncomfortable development for South Korea. However, given Washington’s strategic shift toward employing U.S. forces on the Peninsula primarily for deterring China rather than focusing solely on the North Korean threat, it is necessary to adopt a more forward-looking perspective. If the strategic and operational center of gravity shifts toward USFJ, South Korea’s risk of entanglement in regional contingencies such as a Taiwan Strait crisis may be reduced. If the alliance evolves to the point where South Korea assumes nearly full responsibility for addressing conventional threats from North Korea, then the transfer of OPCON and the presence of a three-star USFK Commander may be more advantageous from the perspective of South Korea’s military autonomy than maintaining the current four-star joint command structure. If a certain level of U.S. troop presence in Korea is sustained, South Korea takes the lead in addressing conventional threats from the North, and the ROK-U.S. alliance continues to strengthen extended deterrence, then rather than rejecting changes in the U.S. regional force posture, South Korea should adopt an attitude that seeks to make constructive use of them.

2) Review of OPCON Transfer and the Choice of Command Structure

The “conditions-based OPCON transfer” pursued between South Korea and the United States has remained at a stalemate, but if the Trump administration changes its policy orientation, it could proceed rapidly. Among the three phases of certification, the Initial Operational Capability (IOC) has been completed, and the Full Operational Capability (FOC) verification is currently in its final stage. Prior to consultations with the United States on OPCON transfer, it is important to conduct a preliminary review and establish a position regarding the structure of the ROK-U.S. command. Alliance command structures are generally divided into the “parallel model,” where each country exercises independent operational control over its own forces (such as the U.S.-Japan alliance or the U.S.-UK arrangement during World War II), and the “integrated model,” which operates under a single combined commander and combined staff (such as the ROK-U.S. alliance or NATO). When OPCON transfer was first pursued under the Roh Moo-hyun administration, the envisioned structure was a parallel model, but under the Park Geun-hye administration, this shifted toward an integrated model in which the Combined Forces Command (CFC) is maintained while the commander position is assumed by a ROK general.

The two models of ROK-U.S. command structure, namely the parallel and integrated models, each have their own strengths and weaknesses. The parallel model stays faithful to the original intent of OPCON transfer in that it secures full operational control over South Korean forces. However, the existence of two separate command structures within the single theater of the Korean Peninsula is relatively disadvantageous in terms of operational efficiency. On the other hand, the integrated model enhances the responsibility and role of the ROK military in defending the Peninsula, but in terms of fostering the capacity for independent war planning and execution, it falls short of fulfilling the fundamental purpose of OPCON transfer. In particular, in light of the “America First” stance and changed alliance perspective of the Trump era, doubts have arisen regarding the previous assessment that the integrated model, namely the current CFC structure, is militarily more efficient. The current CFC system is based on the concept that, in wartime, large-scale U.S. reinforcements would be deployed from the U.S. mainland to the Korean Peninsula, enabling the two militaries to operate in an organically unified manner. Yet this premise has been increasingly called into question by the Trump administration’s position, which emphasizes that, apart from homeland defense and deterring China, allies should bear primary responsibility for addressing other regional threats. Consequently, the likelihood that the large-scale reinforcement plans for the Korean Peninsula, as outlined in OPLAN 5015, will materialize as originally envisioned is steadily diminishing.

Accordingly, regarding conventional warfare, it has become inevitable for the ROK military to take on an almost exclusive level of responsibility, and in that case, rather than maintaining an integrated model in which the ROK and U.S. forces are bound together, it may be militarily more desirable to build and prepare a parallel structure in which the ROK military leads and U.S. forces provide support. Therefore, ultimately transitioning to a parallel model in which the ROK military takes the lead and U.S. forces play a supporting role is likely to be more consistent with the core intent of OPCON transfer and better aligned with the changing trajectory of U.S. defense strategy. Nonetheless, since the shift to a parallel model may raise concerns about weakening of the ROK-U.S. alliance, it is necessary to make continued efforts to strengthen the connectivity of the bilateral command structure, drawing on the development of the U.S.-Japan C2 system as a reference.

5. Conclusion: Forward-looking and Proactive Response to Alliance Transformation

While this report has focused on exploring individual response measures to immediate alliance issues, the three issues are in fact interrelated, underpinned by a broader shift in United States foreign policy orientation during the Trump administration. The greatest challenge confronting the ROK-U.S. alliance lies not merely in pressures related to cost sharing or changes in the size of USFK, but in the widening perception gap between the two countries regarding threat assessments and strategic direction, which constitute the fundamental basis of the alliance. As Washington’s strategic focus shifts from defense against North Korea to the containment of China, questions have been raised about the necessity of large scale ground force deployments, while increasing attention is being paid to mobility and flexibility for operations beyond the Korean Peninsula. This reflects a broader trend that is not limited to the Trump administration. Furthermore, although South Korea is not a free riding country like some European states, it is undeniable that, despite its enhanced national power, it has continued to rely on the United States security umbrella to deter North Korean threats. Given these considerations, rather than focusing solely on immediate issues, it is preferable for South Korea to pursue a broader vision for transforming the alliance on its own terms. Otherwise, there is a risk that the country may become passively drawn into United States demands, resulting in strategically unfavorable negotiation outcomes.

Some argue that in order to prevent strains in the alliance, the South Korean government should concede on defense burden-sharing or align strategically with Washington’s calls for countering China. The intent is to enhance South Korea’s strategic value so as to strengthen alliance cohesion and ensure continued U.S. involvement on the Korean Peninsula. However, relying solely on concessions by South Korea cannot prevent changes in the alliance emanating from Washington, and the proposal for strategic alignment risks confusing means with ends, thereby harming the country’s overall national interests. In particular, even as greater responsibility for the defense of the Korean Peninsula is being placed on South Korea, and even as a reduction in the size and role of USFK is being discussed, paradoxically the debate has shifted toward an increase rather than a decrease in defense burden-sharing. This means that South Korea’s responsibility for countering North Korean threats is expanding. At the same time, its territory is increasingly being utilized as a forward base for U.S. efforts to deter China, while the costs of stationing and operating U.S. forces are also likely to rise. The current challenges facing the alliance stem from differences in threat perceptions and priorities between the two sides. From the South Korean perspective, the utility of the alliance (deterring the North Korean threat) is declining, while the costs of the alliance (increased defense burden-sharing, risks of entanglement in U.S.-China conflict) are rising. In such circumstances, if the South Korean government were to insist on maintaining the size of USFK or delaying OPCON transfer as a means of preserving alliance utility, it would likely face unavoidable increases in defense costs and entanglement risks, resulting in a decline in overall national interests.

Accordingly, it is necessary to recognize the reality of Washington’s strategic shift while responding to immediate issues with a vision of an alliance transformation centered on South Korea’s national interests. First, South Korea should actively embrace greater responsibility for the defense of the Korean Peninsula, as remaining complacent within the existing combined defense system is neither realistic nor safe. At least with regard to conventional threats from North Korea, the South Korean government needs to reduce its dependence on the United States and invest in its own defense capabilities. OPCON transfer is no longer a unilateral demand by South Korea, but rather a feasible initiative that can be pursued smoothly in the context of current alliance dynamics. The key task is to overcome the longstanding “prematurity argument” and psychological dependence on Washington that have persisted since the Roh Tae-woo administration nearly forty years ago. Second, despite these self-strengthening efforts, bilateral cooperation remains indispensable in addressing the North Korean nuclear threat. South Korea and the United States must continue existing efforts to enhance the credibility of extended deterrence by expanding intelligence sharing, strengthening joint planning, and institutionalizing crisis communication channels. While skepticism regarding extended deterrence persists, it is important to recognize that extended deterrence is not solely an issue of the bilateral alliance, but also a matter of U.S. global alliance credibility and the sustainability of the nonproliferation regime. Hence, rather than succumbing to excessive pessimism, it is essential to steadily enhance extended deterrence and sustain its deterrent effect against the North. Notably, as long as a certain level of U.S. troop presence is maintained on the Peninsula, the credibility of extended deterrence can be preserved, which is also critical for preventing abrupt shifts in the regional balance of power in Northeast Asia. At the same time, it should be underscored to Washington that drastic reductions to the level of withdrawal would create pressure for nuclear armament in South Korea, and the South Korean government should also seek to secure indigenous enrichment capabilities, including through the future revision of the ROK-U.S. Nuclear Cooperation Agreement. Third, regarding the containment of China, while it is impossible to deny the strategic orientation of Washington, South Korea should seek to preserve its diplomatic autonomy by setting clear limits and avoiding excessive entanglement, and both governments need to explore a balanced compromise regarding the extent of demands and concessions each can reasonably make.

If Washington’s demands materialize, changes may include a reduction in the size of USFK, the transfer of OPCON, and an elevation of the relative status of USFJ. Yet these should be understood as inevitable alliance transformations shaped by U.S. strategic shifts and South Korea’s growing capabilities. Even under such changes, however, there remain clear common denominators that underpin the mutual interests of both allies. The deterrence of North Korea’s nuclear program and the preservation of stability on the Korean Peninsula, the prevention of a nuclear domino effect in Northeast Asia, and the avoidance of abrupt regional power shifts are shared strategic objectives of South Korea and the United States. Therefore, the two countries must ensure that the core foundation of the alliance does not erode, through deepening extended deterrence and sustaining the presence of U.S. forces in Korea. In an era of systemic transformation in the international order, it is essential to accept the possibility of major changes in the military landscape of the Indo-Pacific, to seize the opportunity presented by alliance transformation, and to respond in a forward-looking and proactive manner.