Pathways for U.S.-ROK-Japan Cooperation
Strengthening Trilateral Ties amid Uncertainty

U.S.-ROK-Japan Trilateral Cooperation: Past, Present, and Future
Kuyoun Chung

How to Consolidate U.S.-ROK-Japan Cooperation under the New Leadership Changes
Eunmi Choi

Beyond Historical Memory: South Korean Domestic Polarization and U.S.-ROK-Japan Trilateral Cooperation
Darcie Draudt-Véjares

Beyond Security: Human Rights as the Foundation of Japan-ROK Cooperation
Yukie Sato

Navigating Uncertainty: Risk Management in U.S.-ROK-Japan Trilateral Cooperation
Jahyun Chun

U.S.-ROK-Japan Trilateral Engagement on Economic Security: Disentangling Resilience, Competitiveness, and Protection
Kristi Govella

Enhancing U.S.-ROK-Japan Cooperation in Maritime and Economic Security
Shino Watanabe

Defending Energy Security Pathways: U.S.-ROK-Japan Strategic Cooperation
Kayla Orta

Trilateral U.S.-ROK-Japan Cooperation on the DPRK Cyberthreat
So Jeong Kim

How Will Trump’s Second Presidency Shape U.S.-ROK-Japan Trilateral Cooperation on North Korea?
Ellen Kim

The Implications of U.S.-ROK-Japan Trilateral Exercises as Strategic Communications
Shin-ae Lee

The Second Trump Administration and the U.S. Indo-Pacific Military Alliance System
Jessica Taylor

Command and Control: Cooperation and Sovereignty in U.S.-ROK-Japan Relations
Sayo Saruta

Conventional-Nuclear Coordination as a Way Forward for U.S.-ROK-Japan Trilateral Security Cooperation
Bee Yun Jo

Trilateral U.S.-ROK-Japan Cooperation on Noncombatant Evacuation Operations
Yurika Ishii

U.S.-ROK-Japan Trilateral Cooperation: Past, Present, and Future

by Kuyoun Chung

As Donald Trump’s second presidency begins in January 2025, the entire world is attuned to what changes to U.S. foreign policy might be wrought under his slogan “Make America Great Again.” This concern stems from the “America first” approach to foreign policy from his first term as president in 2017–21. Key aspects of this foreign policy included a transactional approach to alliances, a rejection of multilateralism, anti-intellectualism, attempts to decouple the United States and China, and populist-driven anti-immigration policies. During his 2024 presidential campaign, President Trump emphasized strengthening the U.S. manufacturing base through a trade war with China, ending so-called forever wars, and protecting national borders.[1] His stance reflected a populist economic nationalism that capitalized on domestic economic scarcity. In foreign policy, he adopted a geoeconomic perspective, promoting a foreign policy based on reciprocity and retrenchment in the Middle East and Europe to focus on competition with China.

The issue lies in the fact that, as Trump fixates on these geoeconomic interests, U.S. allies are worried about the future of the regional security architecture. This is due to the tension between the Trump administration’s goal of gaining an advantage in U.S.-China competition, its retrenchment foreign policy orientation, and its transactional approach to alliances. Specifically, the Republic of Korea (ROK, or South Korea) and Japan are concerned about the administration’s potential impact on trilateral cooperation between the United States, South Korea, and Japan, which is a key component of the security latticework the Biden administration built. Since their first trilateral summit at the 1994 APEC meeting in Jakarta, cooperation between these three countries has often fluctuated. However, the Camp David Declaration agreed on by the three governments in 2023 marked the highest level of cooperation to date. This concord was made possible by the shared strategic interests of the three countries in jointly addressing the North Korean nuclear threat, as well as by South Korea’s foreign policy vision, which aims to position the country as a global pivotal state and engage more actively with the Indo-Pacific region. In fact, the rapidly changing regional balance of power in the Indo-Pacific; the strengthening of alignments among revisionist states such as China, North Korea, Russia, and Iran; and the need for a unified response to these developments have further solidified the value of trilateral cooperation.

In this context, this essay reviews the achievements of U.S.-ROK-Japan trilateral cooperation to date and examines the conditions under which momentum for such cooperation might be sustained during the second Trump administration, setting the stage for this Asia Policy roundtable. This collection of essays by experts from the three states aims to contribute to the effort of cooperation between South Korea, the United States, and Japan by suggesting both new and traditional areas where trilateral cooperation could bolster the regional environment for economic development and resilient security. Through the efforts of all three partners, it is expected that trilateral cooperation can endure in the Trump 2.0 era.

Trilateral Cooperation in the Past

Trilateral cooperation between South Korea, the United States, and Japan began as a platform for addressing the North Korean nuclear issue, with the joint operation of the Trilateral Coordination and Oversight Group in 1999. However, this initiative faced challenges, as the strategic interests of the three countries regarding the resolution of the North Korean nuclear issue did not align precisely. Despite the advancement of North Korea’s nuclear capabilities and the increasing frequency of its provocations, little progress was made in formulating trilateral responses.

In particular, in the early 2000s, South Korea focused on improving relations with China, hoping that Beijing would play a constructive role in addressing the North Korean nuclear issue.[2] In 2013, under President Park Geun-hye, South Korea proposed the Northeast Asia Peace and Cooperation Initiative, emphasizing a parallel strategy of improving both ROK-China and ROK-U.S. relations, rather than expanding ROK-U.S.-Japan cooperation. In a period when U.S.-China competition was beginning to intensify, Park’s regional strategy caused South Korea to lose leverage over the United States, while at the same time Japan’s strategic relations with the United States were strengthening. The Abe administration in Japan aligned with the Obama administration’s rebalancing policy and participated in the U.S.-led Trans-Pacific Partnership, while also enhancing Japan’s security contributions, including the revision of security legislation to permit collective self-defense and a prominent role within the U.S.-Japan alliance. Nevertheless, President Park maintained a critical stance toward Japan on the controversial historical issues between the two countries and rejected a summit with Japan. Although an agreement was reached in 2015 on the issue of “comfort women,” it faced backlash from the South Korean public. As a result, ROK-U.S.-Japan cooperation struggled to regain momentum.

The subsequent administration of President Moon Jae-in in South Korea declared that it would not accept the 2015 agreement, further cooling ROK-Japan relations. In 2018, several events occurred that deepened the emotional confrontations and distrust between the two countries and brought ties to a new low: the dissolution of the Reconciliation and Healing Foundation, the South Korean Supreme Court’s ruling on forced labor during World War II, Japan’s provocative low-altitude flights by Maritime Self-Defense Force aircraft near ROK naval ships, radar lock-on incidents by the ROK Navy, and disputes over listing Japan’s Hashima Island as a UNESCO World Heritage site.

In short, the deterioration of ROK-Japan relations, combined with the rise of U.S.-China competition, caused ROK-U.S.-Japan cooperation to suffer. ROK-Japan relations were even described as the “weak link” in the trilateral cooperation.[3] However, the reluctance of the United States to become entangled in the disputes between its two allies made the U.S. rebalancing strategy and subsequent effort to revitalize trilateral cooperation less tenable.[4] Consequently, the justification for trilateral cooperation on the North Korean nuclear issue weakened from South Korea’s perspective, as the belief emerged that the lever for engaging North Korea in dialogue on denuclearization lay not in strengthening trilateral cooperation but rather in improving ROK-China relations. These factors ultimately led to a situation where the strategic value of ROK-U.S.-Japan cooperation became difficult to enhance.

Current Progress

Although ROK-U.S.-Japan cooperation was initiated in the 1990s to address the North Korean nuclear issue, the formation of the trilateral relationship in fact predates this challenge. It is composed of the U.S.-ROK alliance and the U.S.-Japan alliance. South Korea and Japan are not bound by any formal alliance, but this virtual alliance[5] between them can be traced back to the existence of the Korean Clause in the 1960 revision of the U.S.-Japan Security Treaty, the U.S.-Japan Status of Forces Agreement related to the stationing of UN Command (UNC) forces in 1954, and the fact that Japan has hosted the UNC-Rear since 1957 in support of potential contingencies on the Korean Peninsula.[6]

As North Korea’s nuclear and missile capabilities have advanced, the imperative for ROK-U.S.-Japan cooperation has only increased. Recently, efforts to revitalize the UNC have also been initiated by United States Forces Korea, which aligns with the Yoon Suk Yeol administration’s intention to strengthen the deterrence architecture toward North Korea. In other words, by not only reinforcing the U.S.-ROK alliance but also building a deterrence architecture that encompasses UNC member states, the South Korean government aims to prepare for both North Korean nuclear and missile threats and potential contingencies on the peninsula, while simultaneously showing a united stance by the international community toward North Korea.

This intention is closely tied to South Korea’s first-ever Indo-Pacific strategy and aligns with ROK-U.S.-Japan cooperation as a key component within the broader networked Indo-Pacific security architecture, including minilateral cooperation frameworks such as the Quad, the AUKUS (Australia-UK-U.S.) partnership, the U.S.-Japan-Australia trilateral, and the U.S.-Japan-Philippines trilateral. The presentation of the Indo-Pacific strategy was part of the Yoon administration’s foreign policy vision that the country would be a global pivotal state. As such, ROK-Japan rapprochement and the revitalization of ROK-U.S.-Japan cooperation are integral to the implementation of South Korea’s Indo-Pacific Strategy. Furthermore, the strategy coincided with Washington’s recognition of ROK-U.S.-Japan cooperation as the indispensable foundation for maintaining both a U.S.-led, rules-based order and a balance of power in East Asia.

The 2023 Camp David Declaration, agreed on by Prime Minister Fumio Kishida, President Yoon, and President Joe Biden, encompasses broad cooperation on a range of issues from military affairs to economic security, to human exchanges to technological collaboration. Regarding the North Korean nuclear issue, the three governments established a framework for cooperation on integrated deterrence, including real-time missile-warning information sharing and a trilateral dialogue on space security. They agreed on opposing China’s efforts to alter the status quo in the Indo-Pacific region and issued a joint message to this effect, including an emphasis on the peaceful resolution of the Taiwan Strait issue, which is considered essential for international security and prosperity. The three leaders pledged to expand cooperation across sectors, including enhanced information sharing in the economic domain and the launch of an early-warning system for supply chains.

The declaration recognized that trilateral cooperation will not reach the deeper level of the bilateral U.S.-ROK or U.S.-Japan alliances and is not a binding security alliance to replace them. Nonetheless, the strategic value of trilateral cooperation has significantly increased as the intersection of the three countries’ strategic interests has expanded and been acknowledged. Given the intensification of U.S.-China competition, North Korean provocations, and deepening North Korea ties with China and Russia, the strategic imperative for ROK-U.S.-Japan cooperation is clearly advancing forward.

Looking Ahead

The key factor in making ROK-U.S.-Japan cooperation sustainable is the shared threat perception toward North Korea and China. North Korea has recently proposed a “two-state system” on the peninsula to justify its potential use of nuclear weapons against South Korea. Meanwhile, China is expanding its activities to alter the status quo in the western Pacific, alongside its military buildup. Growing strategic cooperation between China, North Korea, and Russia has further underscored the imperative for ROK-U.S.-Japan cooperation.

However, the strategic value of cooperation between the three states depends on whether it becomes institutionalized in the future. In this context, the potential improvement of ROK-Japan relations is critical. The current rapprochement is largely due to a shared focus on common strategic interests, both states’ identities as democracies, and a strategic priority to restore and maintain a rules-based order, rather than being primarily driven by any true resolution of the protracted historical issues between the two countries. Changes in domestic politics could reverse the current momentum. In this context, Yoon’s declaration of martial law, subsequent impeachment in December 2024, and resulting domestic political uncertainty are of great importance. Politics in South Korea are highly polarized, and foreign policy is similarly divided, as Yoon’s foreign policy perspective is very different from that of the opposing Democratic Party. In particular, there is a stark contrast in their views on ROK-Japan relations. Nonetheless, the perception of the relationship with Japan at the elite level of the Democratic Party differs from that of South Korean public. The public is generally supportive of trilateral cooperation between South Korea, the United States, and Japan to deter North Korean provocations, and it also distinguishes between historical issues and the need for strategic cooperation when it comes to ROK-Japan relations.[7]

Another challenge to the institutionalization of ROK-U.S.-Japan cooperation is the Trump 2.0 era. If the second Trump administration adopts a transactional, bilateral approach to alliances under an America-first stance, as Trump as threatened to do, the durability of the Indo-Pacific as a strategic space could weaken. This could result in the Indo-Pacific strategies adopted by the U.S. allies becoming ineffective, and they might turn to unilateral strategies in an attempt to best secure their own interests, leading to the collapse of the rules-based order. To avoid such a situation, it is imperative that South Korea, Japan, and the United States continue sustaining the momentum of their cooperation and explore new avenues to deepen the three-way partnership. This Asia Policy roundtable collects the perspectives of various experts for this purpose and, in doing so, hopes to provide another novel opportunity for trilateral cooperation.

 
Kuyoun Chung is an Associate Professor of Political Science at Kangwon National University (South Korea). Her research focuses on U.S. foreign policy and security issues in the Indo-Pacific, including alliance politics, regional security architecture, maritime security, and emerging technologies.

Eunmi Choi is a Research Fellow at the Asan Institute for Policy Studies (South Korea). Her main areas of research interest are Korea-Japan relations, Japanese politics, diplomacy, and multilateral cooperation in Northeast Asia. Dr. Choi is a member of the advisory committees to the ROK Ministry of Foreign Affairs, Ministry of National Defense, and National Security Office.

Darcie Draudt-Véjares is a Fellow for Korean Studies in the Asia Program at the Carnegie Endowment for International Peace and a Nonresident Fellow at the National Bureau of Asian Research (United States).

Yukie Sato is a PhD Candidate in the Graduate School of Political Science at Waseda University (Japan). She specializes in the history of ROK-U.S. relations, history of modern Korean political thought, and transitional justice studies.

Jahyun Chun is an Associate Professor in the Department of International Relations at Yonsei University, Mirae Campus (South Korea). Her research interests include international reconciliation and foreign policy in East Asia. Her publications include “Understanding Mistrust and Instability in East Asia” in Pacific Affairs (2022), “Varieties of International Reconciliation” in International Relations (2022), and “Who Decides Foreign Policy? The Role of National Trauma in Shaping the Influence of Public Opinion in South Korea” in Policy Studies (2021).

Kristi Govella is Associate Professor of Japanese Politics and International Relations in the Nissan Institute of Japanese Studies and the Oxford School of Global and Area Studies at the University of Oxford (United Kingdom).

Shino Watanabe is Professor in the Faculty of Global Studies at Sophia University in Tokyo (Japan).

Kayla Orta is the Senior Associate for Korea at the Wilson Center’s Hyundai Motor–Korea Foundation Center for Korean History and Public Policy in Washington, D.C. (United States). She is a former U.S. Department of Defense NSEP Boren Scholar to South Korea and the lead editor of Avoiding Meltdowns and Blackouts: Confidence-Building in Inter-Korean Engagement on Nuclear Safety and Energy Development (2023).

So Jeong Kim is a Senior Research Fellow of the Institute for National Security Strategy (South Korea) and a Nonresident Adjunct Fellow at the Center for Strategic and International Studies.

Ellen Kim is a Senior Fellow with the Korea Chair at the Center for Strategic and International Studies (United States).

Shin-ae Lee is a Research Fellow in the Security Studies Program at the Sasakawa Peace Foundation and a part-time Lecturer at Tokyo University of Foreign Studies (Japan). Her expertise includes Japanese security and foreign policy, security issues on the Korean Peninsula, and strategic communications.

Jessica Taylor is a Senior Advisor to the U.S. Under Secretary for Arms Control and International Security, a U.S. Air Force Reserve Logistics Readiness Officer, and a PhD Candidate in the Security Studies Program at Princeton University’s School of Public and International Affairs (United States). During her previous civil service, Major Taylor served on the headquarters staffs of United Nations Command, ROK/U.S. Combined Forces Command, and U.S. Forces Korea.

Sayo Saruta is President of the New Diplomacy Initiative (Japan) and an attorney at law in Japan and New York State. Her area of specialty is U.S.-Japan relations, including the U.S.-Japan diplomatic system.

Bee Yun Jo is an Associate Research Fellow at Korea Institute for Defense Analyses (South Korea) and a Nonresident Senior Fellow at the Atlantic Council.

Yurika Ishii is an Associate Professor at the National Defense Academy (Japan). Her areas of interest include international law, the law of the sea, and international/transnational criminal law.

Endnotes

[1] Peter Navarro, The True Meaning of Trump’s MAGA: Lessons from the 2022 Republican Red Wave That Never Happened (New York: Bombardier Books, 2023); and Robert C. O’Brien, “The Return of Peace Through Strength: Making the Case for Trump’s Foreign Policy,” Foreign Affairs, June 18, 2024.

[2] Gilbert Rozman, Sue Mi Terry, and Eun A. Jo, South Korea’s Wild Ride: The Big Shifts in Foreign Policy from 2013 to 2022 (London: Routledge, 2023), 16–19.

[3] Wooseon Choi, “New Horizons in Korea-U.S.-Japan Trilateral Cooperation,” Center for Strategic and International Studies, June 27, 2024, https://www.csis.org/analysis/new-horizons-korea-us-japan-trilateral-cooperation.

[4] Kiichi Fujiwara, “Rebalancing and Entanglement: America’s Dilemma in East Asia,” in Asia’s Alliance Triangle: U.S.-Japan-South Korea Relations at a Tumultuous Time, ed. Gilbert Rozman (New York: Palgrave Macmillan, 2015).

[5] Ralph A. Cossa, “U.S.-ROK-Japan: Why a ‘Virtual Alliance’ Makes Sense,” Korea Journal of Defense Analysis 12, no. 1 (2000): 67–86.

[6] Yasuyo Sakata, “Camp David and U.S.-Japan-ROK Trilateral Security and Defense Cooperation: Consolidating the Northeast Asia Anchor in the Indo-Pacific,” Korea Economic Institute, 2024 Korea Policy, vol. 2, no. 1, 2024.

[7] Sangmi Jeong, “Security Threats and South Koreans’ Perception of Japan: Assessing Public Opinion on ROK-Japan Relations and the ROK-U.S.-Japan Security Cooperation,” Korean Journal of International Relations 63, no. 1 (2023): 177–219.