US-ROK Strategic Dialogue: Recalibrating Deterrence Against An Evolving DPRK Nuclear Threat

Executive Summary

In March 2021, the Stimson Center’s 38 North Program, sponsored by DTRA’s Strategic Trends Research Initiative within the US Department of Defense, launched a year-long US-ROK bilateral Track 2 dialogue to consider ways in which the extended deterrence arrangement could be modified in the coming years and to assess the potential effectiveness of various measures in enhancing deterrence against a DPRK attack and providing reassurance to South Korea of the US commitment and ability to respond in the ROK’s defense in case of deterrence failure. Participants came from a diverse range of functional and regional expertise across a broad spectrum of political viewpoints and included both senior-level experts and emerging scholars with diverse backgrounds.

Throughout the dialogue, common threads emerged across US and ROK perspectives, highlighting the careful balance required to properly prepare for and address the issues at hand.

Discussions stressed an urgent need for improved strategic communications about alliance cooperation. There is little public understanding of the breadth of alliance cooperation and consultation that currently takes place, especially regarding extended deterrence. High-profile meetings between defense ministers or military leaders are reported on but do not convey a sense of deep cooperation when the cameras go dark. As tensions rise globally and US policy priorities adjust to world events, there is reassurance in increasing the visibility of working-level cooperation, demonstrating that the alliance is not just strong, but also adapting to the changing security environment.

The range of potential new ways conflict could unfold in the region due to evolving threats requires modifications to conventional weapons employment, war planning, and joint military exercises. Contingency planning for the use of tactical nuclear weapons, cyber attacks on military or civilian facilities, or even the potential for North Korea to initiate an attack amid other conflict in the region all pose complications for allied responses. Planning, practice and especially exercising to failure can help identify operational and command and control challenges for the alliance to prepare for any threats.

Finally, the change in administration in Seoul provides new opportunities to deepen and strengthen alliance cooperation and potentially trilateral US-ROK-Japan security cooperation as well. However, in the current strategic environment, China will likely view moves to deepen regional cooperation and integration among US allies with great suspicion. Knowing Beijing is able and willing to use its economic and political power to impose hardships on Seoul—and other allies that engage in major trade with China—over alliance defense decisions, the United States, South Korea and other allies should develop a collective response strategy to help mitigate the effects of Chinese economic coercion.

Key recommendations include:

Build a comprehensive and coordinated strategic communications strategy that engages stakeholders and the public in more frequent and specific ways surrounding alliance cooperation, coordination and its evolution to build greater confidence that the alliance is adapting to the changing conditions. This means creating greater visibility into the consultative process, cultivating a more-informed press corps about the various ways in which consultation and cooperation are ongoing and coordinating messaging between Washington and Seoul to avoid the appearance of cleavages in policy positions that can be exploited.

Invest in long-term ROK capacity-building on nuclear policy and extended deterrence, engaging a wide range of policy analysts, opinion leaders and emerging scholars through specialized in-person professional development and educational programs, online courses and longer-term Track 2 dialogues. This will help shape public perceptions and discourse over time.

Increase working-level cooperation in the consultative process to help promote the institutionalization of knowledge. While high-level engagements are important for agenda setting and demonstrating the commitment of both sides to mutual defense, a greater emphasis is needed on working-level cooperation. Creating joint studies and allowing more flexible execution of meetings can help facilitate greater learning and exchange and feed recommendations into the higher-level meetings to maximize their utility.

Inject new and realistic scenarios into US-ROK joint military exercises and tabletop exercises (TTXs) to help identify vulnerabilities and areas needing improvement. Wargaming and exercising to failure on both North Korea-specific and broader regional conflict scenarios can reveal where current capabilities and protocols need to be bolstered to be better prepared for conflict and a range of contingencies.

Build an alliance support and response strategy in the case of Chinese economic coercion that utilizes all aspects of state power and galvanizes a collective response among like-minded states. As US-China competition intensifies, China is likely to view changes to the US-ROK alliance posture and deployments with great suspicion and react in a similar, if not a more pronounced, manner. A coordinated alliance response plan may help to prevent coercive actions from being exercised or can at least mitigate their effects.

Build greater trilateral security between the United States, South Korea and Japan to enhance deterrence, recognizing there will be limits to this cooperation in the long run. Focus on areas where trilateral cooperation is imperative to extended deterrence and facilitate high-level dialogue, as well as within Track 2 circles, to build broader support for sustained security cooperation regardless of shifting political dynamics.

Dialogue Background

The nature of the Democratic People’s Republic of Korea’s (DPRK or North Korea) nuclear and missile capabilities has significantly evolved since the United States first established an extended deterrence arrangement with the Republic of Korea (ROK or South Korea). In 2017, the DPRK conducted its first intercontinental ballistic missile (ICBM) test launches, demonstrating limited success. This milestone fundamentally changed its strategic options, adding a new dimension to US and ROK deterrence calculations.

With progress on North Korea’s denuclearization unlikely for the foreseeable future and continued advancement of its weapons of mass destruction (WMD) capabilities, the United States and South Korea need to reassess their current extended deterrence arrangement and adapt to this new reality.

In March 2021, the Stimson Center’s 38 North Program, sponsored by DTRA’s Strategic Trends Research Initiative within the US Department of Defense, launched a year-long US-ROK bilateral Track 2 dialogue to consider ways in which the extended deterrence arrangement could be modified in the coming years and to assess the potential effectiveness of various measures in both enhancing deterrence against a DPRK attack and providing reassurance to South Korea of the US commitment and ability to respond in the ROK’s defense in case of deterrence failure.

The project was designed as a series of virtual roundtable discussions meant to promote a frank and open bilateral dialogue, improve understanding of how participants from each country viewed threats in the current strategic environment and how well–equipped the alliance is to counter them, and assess the potential benefits and risks of certain measures. Participants included a diverse range of functional and regional expertise across a broad spectrum of political viewpoints and included both senior-level experts and emerging scholars.

For each roundtable, 38 North commissioned experts to design a future-oriented scenario of an alternative defense arrangement to help frame the discussion in a common set of assumptions. Discussions examined the pros and cons of the hypothetical scenario, including structural challenges to implementation, domestic political considerations, the potential impact on either deterrence or assurance and possible responses from external actors.

The scenarios featured both nuclear and conventional modifications that have been raised as possible alternative defense arrangements. They were: 1) establishing a bilateral nuclear consultative mechanism; 2) forward deploying US nuclear weapons in Northeast Asia—such as in Japan or sea-based—but not on the Korean Peninsula; 3) forward deploying US nuclear weapons onto the Korean Peninsula; and 4) deploying US advanced conventional capabilities onto the Korean Peninsula and further supporting the rapid development of South Korea’s indigenous conventional forces. The final session in the series then examined China’s possible reactions to the four scenarios to better understand potential challenges or consequences of certain decisions.

Key Insights

In the first session on the prospects of establishing a bilateral nuclear consultative mechanism, there was no common understanding about what this mechanism would entail or what the scope of that consultation would cover. American participants, especially former defense officials, were adamant that peacetime extended deterrence consultation mechanisms already exist and foster robust dialogue and exchange on nuclear policy. However, both US and ROK participants who had not directly participated in those processes were largely unfamiliar with the scope or depth of discussions and exchanges that occur. This lack of transparency—even within the policy community working to support and enhance alliance defense policy and planning—was agreed to be a major problem, one that, if solved, could have reassuring effects for the alliance.

At the same time, both sides acknowledged a high learning curve for South Koreans on nuclear policy that would need to be addressed to facilitate more meaningful cooperation. The dialogue revealed widespread misperceptions of the powers and privileges within other nuclear consultative mechanisms like the Nuclear Planning Group (NPG) at the North Atlantic Treaty Organization (NATO). US participants emphasized how the NPG serves more as a forum for policy discussions, similar to the role of the Deterrence Strategy Committee (DSC) within the current US-ROK Korea Integrated Defense Dialogue (KIDD), but does not engage in actual nuclear operations planning. Both sides acknowledged that while the KIDD does seem to offer a peacetime nuclear consultative mechanism, there is no formal wartime consultation process to enable South Korea to make recommendations to the United States on the potential use or non-use of nuclear weapons. Defining and establishing this process could also enhance reassurance.

The next two sessions considered the deployment of US tactical nuclear weapons, either in the region or on the Korean Peninsula. South Korean participants saw little value in regional deployments. Moreover, there was little consensus on whether US nuclear weapons in South Korea were ultimately beneficial, given the lack of transparency into US command and control and the negative impact this would have on efforts to denuclearize North Korea. Many of the younger ROK participants were especially wary of the implications for denuclearization talks, essentially normalizing nuclear weapons on the Korean Peninsula, and also pointed to potential siting challenges along the lines of local protests over the placement of the Terminal High Altitude Area Defense (THAAD) system. However, they also saw more value in an ROK nuclear deterrent if there were to be nuclear weapons on South Korean soil, to be able to have command and control over their use. Younger ROK participants also highlighted overwhelming public support for South Korea going down that path.

In the final two sessions, there appeared to be wide support for bolstering South Korea’s conventional capabilities. At the same time, ROK participants were skeptical that it would significantly enhance deterrence, also recognizing that the prospects of acquiring US advanced conventional weapons to supplement South Korea’s conventional capabilities would quickly bring Chinese perceptions into the equation. In this context, participants believed that the potential for Chinese backlash to the deployment of US weapons systems, even conventional, was much higher than further development of ROK capabilities, although both would likely be perceived negatively.

China has proved its ability and will to impose economic hardships on South Korea for alliance defense decisions for its decision to deploy THAAD. With US-China competition intensifying, Beijing is likely to view any strengthening of alliance capabilities or further South Korean integration into US missile defenses with great suspicion. South Korean participants were especially adamant about needing a strategy for how to mitigate Chinese economic coercion over South Korea and other US allies, stressing the need for US leadership in those efforts.

The following are some overarching themes that came out of the dialogue.

• The scenarios posed during the dialogues assumed North Korea’s nuclear capabilities would continue to advance. They did not, however, assume major shifts in relations with other regional actors. Certainly, intensifying US-China competition and Russia’s invasion of Ukraine are factors that could drastically change regional security dynamics in the coming years. Furthermore, the push toward re-forming Cold War-era ideological blocs raises questions about how perceptions of North Korea’s nuclear program might change over time, especially depending on how the war in Ukraine concludes. Is there a tipping point at which North Korea’s strategic capabilities become an asset to the smaller authoritarian/undemocratic bloc of states? While the United States and South Korea work to strengthen the alliance against these growing threats, efforts to engage both China and North Korea formally and through informal channels will be important to seek ways to reduce tensions and mitigate the risk of miscalculations or further conflicts.
• North Korea’s nuclear capabilities continue to advance, demonstrating significant progress across a range of conventional and strategic weapons. Notably, North Korea has placed greater emphasis on the development of tactical nuclear weapons in recent months and issued statements expressing a willingness to use them early on in a conflict. This creates a new dimension to potential battlefield conditions should deterrence fail that requires ROK forces and the Combined Forces Command (CFC) to plan and assess accordingly.
• Throughout the course of the dialogue, American participants frequently questioned ROK participants who they considered the target of deterrence: North Korea or China. Most ROK participants viewed North Korea as the target of deterrence as the country’s immediate military threat. While there was a general acknowledgment of a broader regional threat against a rules-based order vis-à-vis China, it was seen in largely political and economic terms. American participants viewed this hierarchy as backward, asserting that deterrence should be targeted toward the broader regional threat, which could also serve to deter North Korea. Based on discussions, it seems unlikely for the ROK calculus to change until the DPRK nuclear threat is diminished.
• In almost every session, a few American participants questioned why there was an assurance problem in South Korea, pointing to US troops on the ground and the many institutions and formal agreements in place. ROK participants brought up North Korea’s increasing ability to threaten both the US and regional targets, which could potentially impede the US’s ability to come to South Korea’s defense in force. They cited examples of DPRK provocations, such as the sinking of the ROK Naval Corvette Cheonan, shelling of Yeonpyeong Island in 2010, and the Demilitarized Zone (DMZ) landmine incident in 2015—and how US leaders at the time appeared more concerned by the escalatory effects of South Korea’s retaliation than the original DPRK provocation. Moreover, anxieties are growing that North Korea would use low-yield nuclear weapons early in conflict or choose to attack alongside the breakout of conflict elsewhere in the region, such as around Taiwan or the South China Sea, with the assumption that US and allied responses and resources would not be as robust to a secondary conflict. While public polling in South Korea shows high public confidence in the capabilities and solidarity of the alliance, there are growing concerns in the ROK defense community about how and if the US would be able to respond to conflict on the Korean Peninsula.
• While the US would like to see comprehensive trilateral cooperation among the US, ROK and Japan, and there are clear benefits to such an arrangement, the relationship between Japan and South Korea will always be fraught with historical disputes. Prioritizing areas of cooperation most vital to collective defense and leaving room to expand when relations improve is a more effective and more sustainable approach than forcing broad trilateral cooperation. That said, with the new administration in Seoul and heightened tensions in the region, there appears to be a new opportunity to revive and deepen high-level trilateral consultations and work toward greater defense cooperation.

Findings and Recommendations

As North Korea’s nuclear capabilities grow and the regional security situation becomes more unpredictable, a comprehensive and coordinated strategic communications strategy is more important than ever.

While it is crucial to reiterate alliance cohesion at the highest levels of government, simply repeating the mantra of being “ironclad” through good times and bad has diminishing value the more it is repeated. Engaging stakeholders and the public in more frequent and specific ways about how the alliance is cooperating will likely build greater confidence that consultation is ongoing and the relationship is adapting to the times.

• Increase public visibility of alliance consultative mechanisms and work: Visibility is key to building public confidence that work is ongoing. Currently, it is difficult to find information about what consultative mechanisms exist, what they do, who is involved in them, and how the pieces all fit together. A bilingual website should be built and maintained that serves as a centralized source of information about alliance defense, extended deterrence issues, and the various bodies that exist to facilitate policy and planning discussions, and an archive of all relevant statements, press briefings, joint studies and communiqués.
• Increase media engagement on alliance management: Media engagement is an effective way to increase public awareness of alliance cooperation, coordination and consultation. Press kits should be developed and distributed ahead of meetings that provide journalists with fact sheets and background materials, as well as a general list of issues that will be covered. This will help equip journalists will the information they need to better understand the nature and significance of various proceedings and provide more informed coverage to the public. A strong communications plan would include cultivating a cohort of trusted journalists to be provided background education on key alliance issues (e.g., through a short intensive course) and who are briefed on a regular basis on key developments—both big and small—and the ways they reflect alliance “combinedness” and evolution.
• Engage key stakeholders inside government, military and Congress on key alliance issues: Improving the psychological aspect of extended deterrence requires engagement of government and military officials, politicians and opinion leaders. This could be accomplished through public and private briefings, reports, exchanges and more hands-on opportunities. Previously, for instance, the US would bring the ROK Chairman of the Joint Chiefs of Staff and National Assembly leaders to show them US strategic capabilities firsthand. Conducting such site visits with joint US-ROK Congressional delegations could have an amplifying effect both in building confidence in the technology and alliance relations as a whole.
• Continue high-level statements of support and solidarity: Political signaling from top leadership can have a reassurance effect when the message has at least some substance and not just repeated slogans, such as “ironclad.”
• Coordinate messaging to both allies and adversaries. Avoid informing allies of policy decisions through the media and surprising one side or the other with new or controversial proposals. Consult or at least notify counterparts of decisions and, as much as possible, coordinate on public messaging. Avoid the appearance of exploitable policy cleavages when messaging to adversaries while still indicating space for diplomacy and off-ramps.

Investment in long-term ROK capacity-building on nuclear policy and extended deterrence will be mutually beneficial.

Capacity-building should not be limited to current alliance managers, but a strategy should seek to engage a wide range of policy analysts, opinion leaders and emerging scholars as well. This will help in shaping public perceptions and discourse over time to create a better understanding not just of the challenges raised by North Korea’s advancing capabilities, but also the ways in which the alliance is responding to the evolving geopolitical conditions. Cultivation down to the university level can help build a pool of better-informed young professionals to populate relevant government and military positions in the future.

• Develop professional development programs for nuclear policy and US-ROK considerations: Develop week-long professional development courses that examine US nuclear policy, its nuclear-sharing arrangements, and the unique circumstances of US-ROK extended deterrence. Similar to the US Department of State’s International Visitor Leadership Program (IVLP), this could target different constituencies, including journalists, policy influencers, academics, young professionals, national assembly staff, and even government officials from non-defense ministries, to gain a better understanding of how the alliance is responding to the security challenges of today. To reach wider audiences, an online version could also be developed that contains a core curriculum on US nuclear policy and customized modules with content specific to the US-ROK, US-Japan, US-Australia, and/or other alliances.
• Institutionalize a Track 2/Track 1.5 dialogue on extended deterrence: Building mutual understanding of evolving threat perceptions and generating ideas on how to move forward together and how various measures could improve or be counterproductive to peace and security on the Korean Peninsula are increasingly important in this strategic environment and should be a sustained effort, not just one-off projects. An ongoing bilateral dialogue at the Track 1.5/2 level could include a core group of regional and functional experts and invite additional subject-matter expertise or demographics to enhance the discussion depending on the topic. Key findings should be documented to help inform future policy planning and foster institutional knowledge. Building deep relationships in the non-governmental space can have a direct impact on future policy, as experts in both the United States and South Korea move in and out of government, even as administrations ebb and flow.
• Sponsor scholarships or special short courses on nuclear policy and extended deterrence for ROK graduate students: In South Korea, education and career paths can be siloed, leading to gaps in understanding between policy and technical communities. Engaging a wide cross-section of ROK students in relevant political or technical studies can help build greater understanding of nuclear policy and extended deterrence challenges from a young age, creating a pool of better-informed young professionals going into government or military positions and feeding into public discourse surrounding alliance health and future direction. To reach wider audiences, an online course could also be developed, with customizable content geared toward a more academic audience. This could be done stand-alone or in partnership with universities to offer course credit or certification for completion. This type of engagement could start as a bilateral initiative and be expanded to include students from other allied countries as well.

Increasing working-level cooperation in the consultative process can help promote the institutionalization of knowledge over time.

The current structure for extended deterrence consultation is driven by a series of high-level meetings, including at the ministerial and deputy minister (ROK)/deputy assistant secretary (US) levels. While high-level engagements are important for agenda setting and demonstrating the commitment of both sides to mutual defense, a greater emphasis is needed on working-level cooperation. In the current structure, cooperation can easily be overwhelmed by meeting preparations and creating the right optics, distracting from meaningful dialogue and exchange. Creating joint studies and allowing more flexible execution of meetings can help facilitate greater collaboration and mutual understanding and feed recommendations into the higher-level meetings to maximize their utility. That said, if the security situation continues to worsen, working toward creating a permanent alliance defense coordination body, similar to the NATO Nuclear Policy Group, with permanent professional and support staff, could help counter problems associated with frequent working-level staff rotations in both the US and ROK, expand cooperation on a day-to-day level, and spearhead public education and outreach efforts.

• Maintain Security Consultative Meeting/Military Committee Meeting (SCM/MCM) and 2+2 meetings: The annual meetings of defense ministers (SCM) and military leaders (MCM) are important to setting the overarching goals and agenda for the extended deterrence dialogues. The combined meeting of ministers from defense and foreign ministries (2+2) demonstrates high-level commitment to alliance cooperation.
• Create greater flexibility within the KIDD and associated committee meetings and build in more working-level cooperation: Instead of intensive two- or three-day consultations across the range of issues covered in the KIDD, enable the various committees the flexibility to conduct stand-alone meetings, with both in-person and virtual options. This would allow the focus to be placed on issue areas rather than the logistics of a multi-day, high-profile meeting. Conducting joint studies on key deterrence issues is also a good way to promote working-level learning, exchange and cooperation, and should be commissioned on a regular basis. KIDD meetings can be used to then discuss the findings and recommendations, working through points of disagreement to enhance mutual understanding.
• Build in top-level leadership signaling: In addition to the SCM/MCM and 2+2 meetings, annual briefings to the two presidents about trends in alliance threats and various modes of cooperation across functional areas could help keep leaders engaged and provide high-level talking points about the strength of the alliance and its cooperation to the public beyond the over-used mantra of being “ironclad.” The more buy-in from top leadership in both Washington and Seoul, the more sustainable and influential the coordination bodies will be over time. Top-level engagement may also serve to facilitate longer-term planning and policies that can be sustained through political transitions of power in both countries.
• Work toward establishing a permanent body that supports alliance defense policy coordination: Creating a permanent body to deal with alliance defense policy and planning issues could be beneficial in the long term. A defense coordinating body that included South Korea, Japan and possibly Australia could facilitate and improve both bilateral and multilateral consultation and cooperation. At the working level, this body would have permanent professional and support staff, with political appointees in key leadership positions. This would allow for expertise and institutional knowledge to be developed and replicated and create a permanent body to conduct public outreach and education.

Injecting new and realistic scenarios into US-ROK joint military exercises and tabletop exercises (TTXs) can help identify vulnerabilities and areas needing improvement.

North Korea’s ability to reach targets in the United States, Guam and Japan has raised concerns over the US’s will and ability to respond with necessary force flows and naval and air assets based in the region. Moreover, as great power competition intensifies, pushing the re-formation of ideological blocs, anxieties are growing about two-front conflict scenarios, either as coordinated or opportunistic actions. As such, wargaming and exercising to failure on both North Korea-specific and broader regional conflict scenarios are important for identifying the vulnerabilities either of capabilities or coordination that need to be addressed.

• Modify existing exercises to include imperfect and challenging conditions and/or non-traditional threat components: Modifying current exercises to include infrequent or cut-off communication from leadership, non-functional equipment, blocked supply chains, early use of low-yield nuclear weapons, or rapid escalation can help measure the alliance’s readiness and ability to respond and adapt, identify areas where training and/or additional resource allocation is needed, and combat complacency during peacetime exercises.
• Develop TTXs that include broader scope or multiple-front conflict: There is growing concern, especially in South Korea, of how North Korea might react if conflict breaks out in the region, such as in Taiwan or the South China Sea—whether the North would take that opportunity to launch an attack on South Korea. Developing TTXs that game out these scenarios would help familiarize all sides with the triggers and challenges of coordination and resource allocations across a range of contingencies.

Further investments in conventional force capabilities are needed to enhance South Korea’s ability to deter and defend against North Korea’s growing capabilities.

South Korea must remain in the strongest possible posture for deterrence to be effective. While North Korea’s deterrence strategy seems to be aimed at creating a sense of equilibrium, South Korea’s further development and deployment of conventional capabilities should be focused on taking away those points that might make North Korea feel optimistic about offensive operations while leaving its defensive tools reasonably intact.

• Further development and integration of ROK conventional capabilities: Further investment is needed to enhance South Korea’s conventional capabilities, especially those designed to directly take away North Korea’s strategic and military advantages, such as supersonic cruise missiles and major enhancements to South Korea’s intelligence surveillance technologies, target acquisition and reconnaissance (ISTAR) integration, and long-range precision strike capabilities. The alliance should also prioritize communication system connectivity and integration, especially C3 (command, control, communication).
• Supplement with US advanced conventional capabilities: US advanced conventional weapons such as drones and long-range precision strike capabilities can complement South Korea’s conventional capabilities. Littoral combat ships and unmanned underwater vehicles could also be useful to help with surface warfare, countermine operations and maritime domain awareness. However, these acquisitions are likely to be met with great suspicion from China and North Korea and are likely to elicit some form of backlash.

Chinese perceptions of deepening US-ROK alliance cooperation may elicit harsher reactions as the US-China rivalry intensifies, requiring a coordinated response plan to potential coercive efforts toward South Korea.

China’s response to South Korea’s THAAD deployment amounted to approximately 8.1 trillion KRW (about 6.7 billion USD) in losses in trade and tourism. This was a stark reminder in Seoul of Beijing’s political will and ability to inflict economic hardship on Seoul for decisions it perceives as going against Chinese interests. As US-China competition intensifies, China is likely to view changes to the US-ROK alliance posture and deployments with great suspicion and react in a similar, if not more pronounced, manner. This means any moves to further integrate South Korea in theater missile defenses, deploy US advanced conventional capabilities or base US nuclear weapons on the peninsula or in the region are likely to trigger coercive actions, even with consultations, and that the alliance should plan potential responses accordingly.

• Build an alliance support and response strategy in the case of Chinese economic coercion: Deepening economic ties between the US and ROK along the lines indicated in the Joint Statement from the 2021 Summit between US President Joe Biden and ROK President Moon Jae-in will be important in reducing China’s overall economic influence. But this is a long-term process. In the meantime, as part of the US integrated deterrence strategy, the US should develop an alliance support and response strategy that utilizes the many tools of state power both at home and among our allies to counter potential Chinese coercion in a collective way. This could include: 1) strong, unified, high-level statements from the US and like-minded countries condemning Chinese coercive actions; 2) rallying of economic and political support in the US and like-minded states to mitigate potential economic losses; 3) reciprocal trade-related sanctions imposed on China by South Korea, the US, and like-minded states (this can be a phased processed, messaging the willingness to do so while China threatens South Korea, and executing only if China does not back down); and 4) encouragement of greater economic cooperation among Indo-Pacific states targeted by Chinese sanctions (in the THAAD case, this included tourism and cultural products). A collective response, or the threat of a collective response, could help counter and potentially mitigate predictable Chinese coercive tactics and open the door to new ways for the US-ROK alliance to evolve.
• Create complementarities between the US Indo-Pacific Strategy and ROK’s New Southern Policy: Building on the 2019 Future Defense Vision of the Republic of Korea (ROK)-US Alliance, the US-ROK Indo-Pacific Strategy-New Southern Policy Dialogue—initiated in August 2020 and released as a joint fact sheet in January 2021—and the Biden-Moon Joint Statement, the alliance should continue to find ways to link and create complementarities between the US Indo-Pacific Strategy and ROK’s New Southern Policy (or follow on strategy under the new administration), stressing the positive values such cooperation upholds rather than framing it as an explicit negation or confrontation with China’s opaque and illiberal approach.

While there is value in trying to increase trilateral cooperation between the United States, South Korea and Japan to enhance deterrence, there will be limits to this cooperation in the long run.

Both the heightened tensions in the region and the change of administration in Seoul create an opportunity to cultivate greater cooperation and coordination between South Korea and Japan in the short term. Efforts to increase security cooperation should be pursued, but with the understanding that pushing for too much up front can create frustration in both Seoul and Tokyo and that historical issues can resurface and disrupt cooperation at any time.

• Focus on areas where trilateral cooperation is imperative to extended deterrence: Focus cooperation around essential security and defense functions, with a clear understanding of what is vital for effective extended deterrence, and scale up when the political environment allows for it. This could include work on improving ballistic missile defense warning, detection and tracking—an issue of growing importance in the current geopolitical environment—and military information sharing. It should also include the development and conduct of trilateral military exercises to better underscore the “combinedness” needed when responding to conflict.
• Facilitate greater dialogue at high and non-governmental levels: Resume trilateral 2+2+2 meetings to get defense and foreign ministers together to stress the importance of trilateral cooperation to collective response and defense. Conduct trilateral Track 1.5 and Track 2 dialogues on extended deterrence as well to facilitate relationship building and mutual understanding among policy shapers and influencers and build support for sustained trilateral security cooperation regardless of ongoing or resurfacing political disputes.
• Use wartime OPCON transition as a springboard for improved trilateral cooperation: Moving toward wartime OPCON transition will require the ROKG and ROK military to confront limits in their ability to lead joint, combined and coalition operations. In addressing such shortcomings and enhancing engagement and communication with the entire American chain of command, ROK commanders will have to broaden their understanding of their growing responsibilities, which will mean increasing and improving cooperation with Japan regarding its crucial role in any crisis or conflict on the Korean Peninsula.

Acknowledgments

This report is made possible with support from the Strategic Trends Research Initiative within the US Department of Defense’s Defense Threat Reduction Agency (DTRA). The Stimson Center’s policies on ethics, independence, and funding are available at https://www.stimson.org/about/transparency/ethics-independence/

The authors would also like to extend gratitude to the dialogue participants and report reviewers for their insights, and a special thanks to Samantha Pitz for her support and contributions to the research.