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I. Introduction: Trump 2.0 and the Transmutation of International Order

The reemergence of President Donald Trump portends profound shifts in the liberal international order and the architecture of global alliances. The second Trump administration, advancing the agenda of “America First 2.0,” is expected to accelerate the restructuring of alliance networks and the redefinition of external relations. This recalibration has triggered the weakening of NATO, stimulated calls for European strategic autonomy, and undermined the perceived credibility of the U.S. nuclear umbrella among Asian allies. The ROK-U.S. alliance and its extended deterrence framework are now approaching a critical inflection point.

The Trump administration consolidated extraordinary foreign policy authority through institutional entrenchment and appointment of loyalists, bolstered by the triumphant 2024 Presidential and congressional elections and his charismatic authority. Backed by the support of the Make America Great Again (MAGA) movement, President Trump has rejected international norms and institutions, repudiated free trade and alliance-based security arrangements, and unilaterally restructured America’s external posture. Consequently, the postwar liberal order led by the United States is disintegrating at a rapid pace, and U.S. allies are increasingly inclined to explore alternative security measures, including nuclear options. Discussions within the Trump administration concerning the termination of the war in Ukraine, a redefinition of relations with Russia, and a renewed focus on national self-interest through European burden-sharing reflect a shifting internal consensus.

Nevertheless, concerns persist that major foreign policy decisions are made by Trump’s own impulsive judgment. His mercurial temperament and top-down decision-making approach amplify uncertainties surrounding U.S. strategic priorities and the coherence of its long-term vision. These concerns are further exacerbated by the potential decline of approval ratings, which could be triggered by economic deterioration, instability in financial markets, or deteriorating relations with traditional allies such as Canada, Mexico, and key European states. In such a context, the trajectory of U.S. foreign policy may become increasingly erratic and difficult to anticipate.

Although the administration currently enjoys considerable political momentum, it often lacks strategic coherence. While the Trump administration perceives China as the primary geopolitical adversary, their goal is to maintain decisive superiority in the great power competition and rise victorious. Trump’s personal affinity for authoritarian leaders such as those of Russia, China, and North Korea introduces the persistent possibility of unexpected deals and negotiations, thereby compounding geopolitical volatility. The full contours of Washington’s China policy have yet to be unveiled. However, once their strategies are made public, they are expected to intensify U.S. responses in high-tech and economic security domains.

Despite these ambiguities, it is likely that Washington will remain committed to countering China’s military expansion through the Indo-Pacific Strategy and by enhancing its forward-deployed force posture in the region. However, by disengaging from transatlantic alliance coordination, Washington has not sufficiently articulated how it intends to achieve effective deterrence against China in the absence of European cooperation. This raises legitimate doubts about whether closer ties between Europe and China would ultimately benefit U.S. interests or bolster its competitive position.

On the domestic front, President Trump has prioritized strict immigration enforcement, including large-scale deportations of undocumented individuals, while implementing protectionist trade policies targeting countries with significant trade surpluses. In one case, tariffs as high as 245 percent have been imposed on Chinese exports. These indiscriminate tariff measures, applied to allies and adversaries alike, have made realignment within the alliance system all but inevitable. While the opacity surrounding tariff implementation and exemptions may grant the United States short-term tactical advantage, it also undermines the credibility of its foreign policy. Over the long term, this approach may erode bilateral partnerships and weaken multilateral bonds, ultimately impairing America’s ability to prevail in strategic competition. The resulting risks include a fragmented Europe, conventional rearmament in major European states such as Germany, nascent efforts to establish a European nuclear umbrella, and an intensifying arms race and deepening anxiety over extended deterrence among U.S. allies in Asia.

II. Trump’s Second-Term Alliance Policy and the Future of Extended Deterrence

1) The Coexistence of Skeptical and Affirmative Views on Alliance Policy

The second Trump administration is accelerating the structural reconfiguration of alliance policy by downgrading ties with Europe while selectively intensifying engagement in Asia. Some European states are actively contemplating the establishment of autonomous nuclear deterrents, and this emerging mistrust may well extend to Asian allies, undermining confidence in U.S. extended deterrence (skeptical view). Conversely, within the Indo-Pacific, the necessity of maintaining allied cohesion to counterbalance China has reinforced the argument for sustaining and strengthening extended deterrence (affirmative view).

The skeptical perspective holds that Washington’s retrenchment from Europe will inevitably extend to Northeast Asia. As European states confront a security vacuum created by U.S. disengagement, they are exploring alternatives such as nuclear sharing and independent deterrence excluding the United States. This shift has sparked concern that such thinking may gain global traction. The Trump administration’s push for an early resolution to the Russia–Ukraine war, its imposition of unilateral territorial concessions on Ukraine, and its calls for regime change in Kyiv reflect a conspicuous tilt toward Russia. Unlike the Biden administration, which reaffirmed commitments made under previous security assurances, Trump’s policy reversal toward Ukraine has raised fears that U.S. security pledges elsewhere could also be withdrawn or renegotiated.

Consequently, several European countries have begun to consider receiving deterrence frameworks independent of the United States (Rose 2025). Among the proposals are efforts to establish a shared European deterrent, leveraging the existing nuclear capabilities of France and the United Kingdom. However, the efficacy of such an initiative remains constrained by the principle of national control, as final launch authority would still reside with national leaders. This structural limitation may reproduce some of the same anxieties currently associated with U.S. extended deterrence.

The United Kingdom, in particular, faces two critical constraints that necessitates its strategic cooperation with the United States. First, it leases Trident missile systems from the United States to reduce defense costs, which necessitates full interoperability between U.S. delivery platforms and British nuclear warheads. This technological reliance entangles the British deterrent posture with U.S. operational frameworks. Second, the United Kingdom continues to experience delays in modernizing its submarine-based deterrent, particularly the replacement of its strategic ballistic missile submarine (SSBN) fleet, raising the prospect of capability gaps in the coming decade.

Furthermore, exploratory comments from policymakers in Ukraine, Poland, and Germany have hinted at the potential pursuit of indigenous nuclear capabilities. However, any such ambitions would confront substantial technical and diplomatic barriers, including fissile material acquisition and weapons development expertise. It remains uncertain whether the United States would tolerate such proliferation without enforcing punitive measures or fully abandoning the alliance structure. Still, some governments appear to interpret Trump’s possible NATO withdrawal and pro-Russian tendencies as signaling the broader unraveling of the European alliance framework. In response, they are investigating nuclear options disconnected from U.S. security guarantees. However, most European states interpret Trump’s posture not as an intent to dismantle NATO but as a call for burden-sharing, which may manifest in increases in defense budgets, contributions to collective defense, and efforts to enhance national military capabilities.

While the debate over a European deterrent has temporarily subsided following the NATO Secretary General’s unequivocal assertion that there is “no substitute” for the American nuclear umbrella,” the potential for renewed discussion remains. Should distrust in U.S. commitments continue to grow among Indo-Pacific states, the ripple effects of Europe’s nuclear discourse could erode confidence in extended deterrence throughout the region. In the Republic of Korea (ROK), calls for an independent nuclear arsenal are gaining traction, citing waning trust in U.S. commitments and the Trump administration’s perceived ambivalence toward nuclear proliferation within allied states.

In contrast to Europe, the Indo-Pacific presents a more favorable context for alliance preservation. While the Trump administration’s broader strategy is grounded in transactional nationalism and selective engagement, its China-focused defense posture necessitates robust cooperation with regional allies. This positive outlook emphasizes that despite President Trump’s political orientation, his administration has consistently supported military modernization and posture enhancement aimed at deterring China. Strategic direction under the second Trump administration suggests a prioritization of the Indo-Pacific over Europe, the formation of anti-hegemonic coalitions, the reinforcement of regional nuclear posture, the modernization of the nuclear triad, and the expansion of low-yield tactical nuclear capabilities.

Elbridge Colby, who leads defense strategy formulation in the second Trump term and formerly served as Deputy Assistant Secretary of Defense, outlined in his 2021 book The Strategy of Denial that Taiwan and the South China Sea represent the most likely flashpoints for conflict. He has called for clearly delineated roles for allies such as Japan, Australia, and the ROK in scenarios involving limited war with China. At a Senate Armed Services Committee hearing on March 4, 2025, Colby responded to questions regarding the value of extended deterrence against North Korea and China by emphasizing the need for a robust and credible posture. He stressed the importance of recognizing threats clearly, ensuring responsibility-sharing among allies, optimizing defense coordination, and maintaining strategic continuity. This suggests that Washington is pursuing differentiated policies toward its European and Asian allies, and that it is highly unlikely to permit nuclear proliferation within its alliances, whether symbolic or substantive, given its overarching goal of preserving hegemonic dominance.

2) Entrenchment of Indo-Pacific Centrism

The second Trump administration is expected to prioritize its Indo-Pacific strategy by advancing the modernization of strategic nuclear forces, redeploying tactical nuclear weapons, and stationing intermediate-range missile systems throughout the region. In particular, increased strategic flexibility for U.S. Forces Korea, the acceleration of wartime operational control (OPCON) transfer, and the reconsideration of tactical nuclear deployment on the Korean Peninsula are likely to emerge as focal policy issues.

While the United States will likely preserve its global extended deterrence framework to support the Nuclear Non-Proliferation Treaty (NPT) and maintain the alliance network, the regional emphasis is anticipated to shift from Europe to Asia. To avoid constraints on its freedom of action, the United States is expected to continue dissuading its Asian allies from pursuing nuclear capabilities while offering extended deterrence as a reciprocal assurance. Once the forthcoming National Defense Strategy is finalized, Washington is projected to center its posture more explicitly on countering China, with an emphasis on strengthening deterrence and defense capabilities.

Under the first Trump administration, deterrence was framed primarily through integration across multiple domains and coordination with allied capabilities. The second administration, by contrast, is likely to pivot toward improving tangible force readiness and expanding forward-deployed assets. Within this framework, despite broader efforts to limit defense expenditures, the United States is expected to proceed with the modernization of key strategic systems, including the Sentinel intercontinental ballistic missile, the B-21 strategic bomber, and the Columbia-class ballistic missile submarine.

Concurrently, the administration is likely to evaluate forward deployment options involving both tactical nuclear weapons and strategic assets to South Korea and Japan. It may also pursue an increase in theater nuclear forces and invest in dual-capable delivery systems capable of launching either nuclear or conventional munitions. In support of these initiatives, Washington could move to expand nuclear weapons infrastructure by raising the annual production of warheads and reviewing the possibility of resuming nuclear testing.

Extended deterrence for East Asian allies is expected to develop further within the broader framework of the Indo-Pacific strategy. The administration’s differentiated posture between European and Asian allies reflects an underlying intent to increase economic and military burden-sharing in Asia. Through this recalibration, the United States seeks to reduce its direct provision of global public goods while reasserting its strategic competitiveness, particularly in its rivalry with China.

Although the principal aim of the Indo-Pacific strategy is to establish a U.S.-led multilateral military arrangement in response to China’s expanding capabilities, the administration has so far refrained from aggressively implementing this multilateral approach within the region.

3) Key Variables Driving Changes in Extended Deterrence Policy

On May 1, 2025, Secretary of Defense Pete Hegseth initiated the 2025 National Defense Strategy (NDS), instructing that it be completed by the end of August. This directive is grounded in the principles of America First and peace through strength, which serve as the ideological foundation of the Trump administration’s second-term defense policy.

However, other strategic documents, including the National Security Strategy (NSS) and the Nuclear Posture Review (NPR), are not expected to be finalized before 2026. In light of this timeline, continued uncertainty regarding alliance management and extended deterrence policy appears inevitable in the short term. Under these constraints, the most effective way to anticipate the direction of extended deterrence in the second Trump administration is to examine key developments emerging during the transition period and the initial phase of the new term.

The first and most significant factor shaping policy is personnel, particularly the president, his advisors, and senior officials, whose preferences will determine policy priorities. President Trump’s distinctive characteristics—transactionalism, populism, amateurism, and a willingness to bluff in pursuit of favorable negotiations—are expected to exert a powerful influence on policy direction. The current team of advisors, largely composed of loyalists, includes both primacists, who favor robust global engagement and military strength, and restrainers, who advocate a narrower focus on homeland defense and countering China. Despite these internal differences, the two camps appear to share a consensus regarding the centrality of China policy. As a result, the absence of significant internal constraints may allow the administration to move decisively and energetically, applying lessons learned during Trump’s first term to pursue more efficient and aggressive implementation.

Domestically, the administration’s chief priorities center on interest rate reductions, stricter immigration enforcement, protectionist tariff measures, and administrative streamlining. The Korean Peninsula henceforth occupies a relatively marginal position within the broader policy agenda. The trajectory of extended deterrence and national defense posture will likely be shaped by several domestic variables, including public satisfaction with economic conditions, the president’s approval rating, the internal cohesion of the MAGA political coalition, and the influence of external shocks.

The second major influence is the bipartisan Congressional Strategic Posture Review conducted in 2023, the second such review in U.S. history following the 2009 iteration (Creedon et al. 2023). The review was prompted by growing concern over the expansion of Chinese and Russian nuclear capabilities, the war in Ukraine, and broader geopolitical instability. The report emphasized the unprecedented challenge of deterring two nuclear peers simultaneously. Key threats identified included China’s rapidly expanding nuclear arsenal, potential military aggression against Taiwan, non-nuclear threats in the cyber and space domains, and Russia’s enhanced strategic military capabilities and aggressive use of force. The commission recommended several core priorities for the period between 2027 and 2035: (1) maintaining strategic deterrence, (2) building capacity for simultaneous deterrence of China and Russia, (3) strengthening alliances and partnerships, (4) modernizing both nuclear and non-nuclear capabilities, and (5) expanding strategic infrastructure. Notably, the report called for a whole-of-government approach to revising U.S. defense strategy and recommended specific measures to enhance extended deterrence, such as reinforcing assurance mechanisms for allies, strengthening the nuclear posture in the Indo-Pacific, augmenting theater-level nuclear capabilities, and addressing gaps in non-nuclear regional forces.

The third influential document is the Heritage Foundation’s Project 2025, which was prepared in anticipation of a second Trump administration (Dans and Groves 2023). This report closely parallels the 2023 Strategic Posture Review and proposes similar policy recommendations. It advocates accelerating modernization of strategic nuclear systems, including the Sentinel ICBM, B-21 bomber, Columbia-class SSBN, and nuclear command, control, and communications (NC3) systems. It also recommends enhancing extended deterrence in Asia through a fortified U.S.-Japan-ROK security cooperative structure U.S.-Japan-ROK, developing a NATO-style framework for extended deterrence collaboration, and encouraging discussions on redeploying U.S. tactical nuclear weapons to South Korea and Japan. The report further urges the resumption of plutonium and uranium production, increasing annual nuclear warhead output from 30 to 80, and reviewing the feasibility of nuclear testing. As part of its broader China containment strategy, it calls for rotational deployment of strategic assets in the region, consideration of intermediate-range missile deployments, enhancement of indigenous defense capabilities in Japan and South Korea, and preparation for potential dual-theater conflicts in Northeast Asia.

The fourth source of influence is the Interim National Defense Strategic Guidance, reported by The Washington Post in late March 2025 (Washington Post 2025). According to this report, Secretary Hegseth identified the prevention of a Chinese invasion of Taiwan and the defense of the U.S. homeland as the administration’s two paramount defense priorities. To achieve these objectives, he announced plans to pressure allies to assume greater responsibility for deterring threats from Russia, North Korea, and Iran. Hegseth further clarified that China constitutes the Department of Defense’s sole pacing threat and that rejecting any fait accompli regarding Taiwan’s absorption into China is central to U.S. defense planning. This guidance reflects a departure from the traditional U.S. role in deterring threats from Moscow and a pivot toward Asia-focused deterrence. The Washington Post noted that this interim guidance closely mirrors the Heritage Foundation’s 2024 report (Velez-Green and Peters 2024), co-authored by Deputy Assistant Secretary of Defense Velez-Green and scholar Robert Peters, which called for a strategy centered on asymmetric capabilities and a force posture optimized for a single major conflict with China. It prioritized arming Taiwan, dispersing and fortifying U.S. operational facilities in Japan, the Philippines, Australia, and Guam, and expanding the U.S. nuclear force to provide limited nuclear options necessary for escalation control and deterrence against Chinese theater nuclear use.

In summary, Trump 2.0 will most probably focus on deterring China and reinforcing homeland defense, while concurrently strengthening nuclear deterrence and expanding allied burden-sharing. These strategic adjustments are likely to have substantial implications for the role of U.S. forces on the Korean Peninsula, South Korea’s defense contributions, and the timeline for OPCON transfer.

III. Outlook for Extended Deterrence on the Korean Peninsula and Policy Challenges

1) Prospects for Extended Deterrence on the Korean Peninsula

Extended deterrence on the Korean Peninsula is expected to be shaped by a complex interplay of challenges and opportunities. In particular, the 2024 Heritage Foundation report offers three key policy recommendations aimed at enhancing deterrence against North Korea, which provide useful insights into the anticipated direction of U.S. policy.

First, the United States should urgently support the deployment and reinforcement of South Korean military capabilities to repel a potential North Korean ground invasion. Second, given the practical limitations of U.S. conventional force deployments in the event of a contingency, the report recommends that the transition of wartime operational control (OPCON) be accelerated so that the ROK Armed Forces can take the lead in countering North Korean aggression. Third, the U.S. Department of Defense is advised to deploy an expanded and diversified array of limited nuclear options, strengthen nuclear coordination with South Korea, reinforce homeland missile defense, and enhance regional missile defense systems to ensure a stronger and more credible posture.

The report underscores the importance of deterring North Korean use of nuclear and WMD capabilities against South Korea or Japan by evaluating credible alternatives if it becomes evident that North Korea can overwhelm or bypass U.S. homeland missile defense. In an additional report published in March 2025, co-author Robert Peters further argued that forward deployment of low-yield, theater-range, non-strategic nuclear weapons tailored to each adversary is essential for deterring China, Russia, and North Korea (Peters and Glickman 2025). He specifically emphasized the need for redeploying U.S. tactical nuclear weapons to the Korean Peninsula to strengthen deterrence against North Korea.

As the U.S. military posture shifts toward a China-centric strategy, the role of the U.S.–ROK alliance and of U.S. Forces Korea is expected to evolve significantly. Rather than reducing regional military assets, the United States is likely to pursue an augmentation of forward-deployed forces to enhance its deterrence capabilities and reinforce its defense posture vis-à-vis Taiwan. In this context, Washington is expected to request greater flexibility for U.S. forces stationed in Korea, ensure their ability to support contingencies in the Taiwan Strait, expand defense-industrial cooperation, reinforce missile defense coordination for homeland protection, and secure increased defense spending and burden-sharing from Seoul. At the same time, rather than linking extended deterrence to cost-sharing negotiations, the United States may focus on enhancing military posture through forward deployment of strategic assets.

Reports indicate that Washington is exploring several regional options to strengthen its strategic deterrence posture. These include the (1) deployment or reinforcement of theater nuclear forces in the region, (2) consideration of redeploying tactical nuclear weapons to the Korean Peninsula, (3) forward deployment of Mid-Range Capability (MRC) missile units, and (4) the application of a NATO-like extended deterrence model. This evolving approach is driven by heightened concerns about the possibility of simultaneous conflicts in East Asia and growing awareness of deterrence gaps resulting from the relative scarcity of theater nuclear assets in the region.

2) Increased Possibility of Tactical Nuclear Weapon Redeployment

Given the growing threat of North Korea’s nuclear weapons and the need to recalibrate the ROK-U.S. alliance, there is a high possibility that discussions on the redeployment of B61-series tactical nuclear weapons to the Korean Peninsula will gain momentum to dispel concerns that the U.S. may abandon its extended deterrence commitment. In such a case, the construction of storage facilities, the establishment of operational systems, and strategic communication with both the public and neighboring countries will be key issues.

The redeployment of tactical nuclear weapons to the Korean Peninsula is likely to emerge as one of the most contentious issues in the ROK-U.S. alliance going forward. Given the current shortage of suitable tactical (non-strategic) nuclear weapons available for deployment by the U.S., the most feasible option in the short term is likely to be the B61-series nuclear bombs, which can be delivered by aircraft. To deploy them, storage facilities and certified dual-capable aircraft must first be in place. In other words, even setting aside political and strategic issues, physical preparations such as storage and hangar facilities, operational personnel, and aircraft must be secured in advance.

At the same time, South Korea must be fully prepared for potential political and social controversies. Sensitive issues such as the redeployment of tactical nuclear weapons and the strategic flexibility of U.S. Forces Korea may provoke unproductive domestic debates and strong backlash from neighboring countries. Therefore, thorough and proactive strategic communication plans must be prepared to address likely opposition from neighboring countries such as China, Russia, and North Korea, as well as to communicate with the South Korean public. The ROK-U.S. alliance may choose to adopt a strict “neither confirm nor deny” (NCND) approach and opt to maintain complete secrecy on the matter. Regardless, this issue undeniably requires closer consultation and coordination between South Korea and the United States than any other.

3) Managing OPCON Transfer in Relation to Extended Deterrence

As the United States calls for expanded strategic flexibility for U.S. Forces Korea and presses for an accelerated transfer of wartime operational control (OPCON), questions surrounding command-and-control structures and the integration of nuclear and conventional operations are likely to become central to alliance management. These developments require comprehensive preparation and careful coordination.

From Washington’s perspective, Seoul should assume greater responsibility for its own defense, and this position may lead the United States to prioritize the transfer of OPCON. The issue of OPCON transfer is closely intertwined with U.S. efforts to expand the strategic flexibility of its forces on the Korean Peninsula. Even if South Korea agrees in principle to these changes, such cooperation should not be misinterpreted as approval of a reduction or withdrawal of U.S. forces. While the possibility of limited adjustments cannot be dismissed entirely, especially if framed as part of an efficiency-oriented force optimization plan, Korea’s geographic proximity to China, the region’s potential for simultaneous contingencies, and the ground-centric structure of U.S. Forces Korea all support the case for maintaining or even enhancing the current force posture. Under these conditions, additional deployment of assets such as the F-35A and high-performance unmanned aerial vehicles remains a feasible option.

The United States is therefore likely to insist on completing the OPCON transfer as a precondition for greater strategic flexibility. This shift would enable South Korea to play a more autonomous role in the event of a contingency. To avoid creating vulnerabilities in the alliance's deterrence posture, the two countries must carefully evaluate whether the necessary conditions for OPCON transfer have been fully met. One of the most pressing challenges involves determining who would retain command-and-control authority over nuclear assets deployed to the Peninsula. This issue must be resolved within the existing framework of the ROK-U.S. Combined Forces Command (CFC), which is expected to remain intact. The process of optimizing the integration of nuclear and conventional forces will require precise calibration between both governments.

In managing the evolution of U.S. Forces Korea, South Korea should respond constructively to U.S. demands while also pursuing countermeasures to preserve the alliance’s deterrent credibility. Given Washington’s growing focus on Taiwan, it is likely to assign expanded regional roles to U.S. forces stationed in Korea in the event of a Taiwan contingency. South Korea must therefore emphasize the strategic importance of its own defense, citing the risks associated with concurrent conflicts. At the same time, it should reject any pressure to contribute additional forces to a Taiwan scenario and instead call on the United States to deploy additional capabilities to Korea. These may include rotational or permanent deployments of new, more advanced systems or the replacement of existing forces with upgraded assets.

Taken together, these developments point to an unprecedented emphasis on alliance coordination and extended deterrence cooperation between Washington and Seoul. It is expected that the allies will continue to rely on existing consultative bodies such as the Nuclear Consultative Group (NCG), the Extended Deterrence Strategy and Consultation Group (EDSCG), and the annual Security Consultative Meeting (SCM). This continuity follows the precedent set during Trump’s first term, when extended deterrence dialogues initiated under the Obama administration were maintained. At present, the two countries are engaged in efforts through the NCG to develop joint operational guidance on nuclear deterrence and operations, with the goal of producing a framework for the combined use of nuclear and conventional capabilities. These efforts must be sustained at the working level across both the defense and foreign ministries.

In response to the escalating North Korean nuclear threat, new areas of policy coordination are likely to emerge, including discussions on redeploying U.S. tactical nuclear weapons and the designation of nuclear command authority in crisis scenarios. One such proposal would assign control over nuclear use to either the Combined Forces Commander or the U.S. Forces Korea Commander in the event of conflict. At the same time, Washington may seek to revise or expand the terms of nuclear cooperation with South Korea to enhance deterrence credibility vis-à-vis China. However, if domestic political instability, such as impeachment proceedings or economic downturn, weakens the Trump administration, concerns over the reliability of U.S. extended deterrence commitments could resurface in South Korea.

4) Decoupling Cost Sharing from Extended Deterrence Policy

The United States’ provision of extended deterrence on the Korean Peninsula must be regarded as a core alliance responsibility and should not be entangled with discussions on increasing South Korea’s financial contributions to defense. In particular, any additional deployment of U.S. strategic assets or reinforcement of the Peninsula’s defense posture should be pursued either as a matter of mutual strategic interest or as part of a broader framework of alliance burden sharing, contingent upon South Korea’s support for expanding the strategic flexibility of U.S. Forces Korea and advancing the transfer of wartime operational control.

Accordingly, in order to safeguard its national interests, South Korea must engage in diplomatic consultations with the United States to ensure that efforts to bolster extended deterrence, including the deployment of supplementary forces or the redeployment of tactical nuclear weapons, are not linked to discussions about increasing South Korea’s financial contributions to the alliance. These initiatives must be clearly presented as reciprocal measures that the United States is obliged to undertake in return for South Korea’s alignment with broader alliance posture adjustments.

To that end, it would be prudent to address these matters within the larger context of U.S. force posture realignment in the Indo-Pacific and evolving frameworks of allied burden sharing. This approach will allow both governments to insulate essential deterrence enhancements from the transactional pressures of budgetary negotiations and preserve the credibility of their strategic commitments.

IV. Conclusion: The Need to Redefine ROK-U.S. Extended Deterrence Cooperation

Security exigencies and contingencies surrounding the Korean Peninsula are becoming increasingly precarious, shaped by anticipated adjustments in U.S. regional force posture, the intensification of Russia-North Korea military collaboration, trilateral strategic alignment among North Korea, China, and Russia, the continued sophistication of North Korea’s nuclear arsenal, and the looming prospect of concurrent contingencies in the Taiwan Strait and on the Peninsula. These converging factors suggest that the second Trump administration will place strategic priority on countering China, thereby reinforcing the United States’ forward military posture across the Indo-Pacific. Within this evolving landscape, Korea is likely to encounter a confluence of exceptional strategic challenges and consequential policy openings.

In response to this heightened uncertainty, South Korea must confront several urgent and interrelated imperatives. Foremost, it must work to institutionalize a robust framework for extended deterrence cooperation with the United States, while carefully calibrating between the demands for enhanced strategic flexibility on the part of Washington and the imperative to preserve credible deterrence vis-à-vis North Korea. This necessitates close coordination on key alliance issues, including the potential redeployment of tactical nuclear weapons, the timeline and conditions surrounding operational control transfer, and the broader parameters of defense burden-sharing.

Moreover, South Korea must prepare for scenarios in which President Trump, driven by political expediency, may choose to instrumentalize joint military exercises or the deployment of strategic assets as bargaining tools in a renewed dialogue with Kim Jong Un. In anticipation of such contingencies, Seoul must assert a more proactive and autonomous role in alliance management, ensuring that its core security interests are neither compromised nor subordinated to transactional diplomacy.

Finally, while the alliance with the United States remains the bedrock of South Korea’s national defense strategy, Seoul must adopt a more assertive and forward-leaning approach in enhancing its indigenous defense capabilities. This includes the development of advanced weapons systems, the expansion of asymmetric assets such as space, cyber, artificial intelligence, and robotics, and the institutional reform of military command structures. In doing so, South Korea can simultaneously address long-standing alliance asymmetries, including the bifurcation of command authority, excessive reliance on U.S. intelligence infrastructure, deficiencies in theater-level operational planning, and the structural rigidity of the upper echelons of the Korean military leadership. ■

References

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Coughlin, Con. 2025. “Delays in Trident renewal put our deterrent in peril” The Telegraph. March 5. https//www.telegraph.co.uk/news/2025/03/05/delays-in-trident-renewwal-deterrent-in-peril/(6.

Colby, Elbridge. 2021. The Strategy of Denial: American Defense in an Age of Great Power Conflict. New Haven: Yale University Press.

Dans, Paul and Groves, Steven, et. al. 2023.“Mandate for Leadership: The Conservative Promise.” Project 2025. The Heritage Foundation.

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Peters, Robert and Eli Glickman. 2025. “Forward Deployment of Non-Strategic Nuclear Weapons Is Needed to Deter Adversary Aggression.” The Heritage Foundation.

Rose, Gideon. 2025.“Get Ready for the Next Nuclear Age.” Foreign Affairs. March 8. https://www.foreignaffairs.com/united-states/nuclear-age-proliferation-trump-nato-gideon-rose

Secretary of Defense. 2025. “Memorandum Directing the Development of the 2025 National Defense Strategy.” May 2. https://media.defense.gov/2025/May/02/2003703230/-1/-1/1/MEMORANDUM-DIRECTING-THE-DEVELOPMENT-OF-THE-2025-NATIONAL-DEFENSE-STRATEGY.PDF

Velez-Green, Alexander and Robert Peters. 2024. “The Prioritization Imperative: A Strategy to Defend America’s Interests in a More Dangerous World.” The Heritage Foundation.

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■ Hyeongpil HAM is Senior Research Fellow at the Korea Institute for Defense Analyses.

■ Translated and edited by Chaerin KIM Research Assistant
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