South Korea–Japan relations: Unresolved issues and ongoing disputes

South Korea and Japan have had tense relations for decades over their unresolved historical and territorial issues. Two major anchors of their ongoing spat are historical issues and territorial issues. First and foremost, South Korea and Japan have disputed whether Japan has sufficiently acknowledged with ‘sincere’ apologies and ‘proper’ management Japan's atrocities and behaviors during its colonial rule over the Korean Peninsula from 1919–1945 and through World War II. Comfort women and wartime forced labor problems, for instance, have been consistent issues of contention between South Korea and Japan. When the Moon Jae-In administration rejected the 2015 deal between South Korea and Japan over the comfort women issue, commenting that it was faulty and did not resolve any problems properly, it provoked Japan tremendously, stirring up great distrust and anger among Japanese people toward South Korea. In 2018, the South Korea's Supreme Court ruled that Japan's Mitsubishi Heavy Industries must compensate 10 South Koreans for their forced labor during Japan's war efforts in 1944.Footnote ² This ruling provoked Japan with further anger and distrust against South Korea, pushing the South Korea–Japan relationship into an almost deadlock situation. When South Korean President Yoon Suk-yeol and Japanese Prime Minister Fumio Kishida announced their future-oriented bilateral relationship beyond historical issues like comfort women and forced labor in March 2023,Footnote ³ there was significant backlash among the Korean people against the Yoon administration, despite the US and Japan's welcoming remarks on such moves. Japanese right-wing politicians have repeatedly endorsed junior high school textbooks where Japan's historical wrongdoings were either completely deleted or modified in their own favor (Yoshifumi Reference Yoshifumi, Nishino, Kim and Onozawa2018). Such moves have led to further anger and distrust among the South Korean people against Japan, worsening South Korea–Japan relations.

Another pillar of South Korea–Japan tensions is the territorial and maritime disputes over the islands of Dokdo/Takeshima and the East Sea/Sea of Japan. South Korean governments’ ongoing position over Dokdo is that South Korea exercises its “irrefutable territorial sovereignty over Dokdo” and thus “no territorial dispute exists regarding Dokdo.”Footnote ⁴ Japanese governments have claimed sovereignty over Takeshima, refuting South Korea's claim over Dokdo.Footnote ⁵ Most recently, in its 2022 National Security Strategy, Japan stated its claim of “the sovereignty of Takeshima” as “an inherent territory of Japan” (Ministry of Foreign Affairs of Japan 2022, 15). South Korea responded by stressing that Japan's repeated claims to Dokdo is “not helpful in the efforts for the establishment of the future-oriented Korea–Japan relationship.”Footnote ⁶ The islands are deeply intertwined with unresolved historical issues and animosities, which results in recurring, hard-to-resolve contentions between South Korea and Japan (Wiegand and Choi Reference Wiegand and Choi2017). Khalil (Reference Khalil2012, 337) notes that for Koreans, Japan's claim of the islands has “ignited deeply ingrained collective memory of past injustice” against South Korea. Such sensitivity toward each other, along with their unresolved historical issues, has made South Korea–Japan disputes over Dokdo/Takeshima almost deadlocked (Kang Reference Kang2010).

As historical and territorial issues disputed between South Korea and Japan are deeply entangled with sovereignty, memory, and even a sense of national pride, nationalism and rally around the flag effect have played significant roles in further amplifying South Korea–Japan tensions (Bong Reference Bong2013; Dudden Reference Dudden2008; Koo Reference Koo2010; Moon and Li Reference Moon and Li2010; Wiegand and Choi Reference Wiegand and Choi2017). When South Korean presidents engaged with the public in narratives about Japan's historic treatment of Koreans, they received higher public opinion poll rating (Hwang, Cho, and Wiegand Reference Hwang, Cho and Wiegand2018). Conversely, in 2012, former South Korean President Park Geun-hye had to withdraw from security information sharing negotiations with Japan due to major domestic pressure (Wiegand Reference Wiegand2015). In Japan, especially since Shinzo Abe's terms, strong nationalist movements have dominated among major politicians and domestic politics in Japan (Nakahara Reference Nakahara2021), which has made Japanese governments more resistant to take any concessions in ongoing disputes against South Korea over any issues.

Asymmetric alliances and the US and South Korea–Japan relations

The US has been a longstanding observer of the “perennially fraught” relationship between South Korea and Japan over their disputed historical and territorial issues (Congressional Research Service 2023, 5) and “long encouraged enhanced South Korea–Japan relations” (Congressional Research Service 2022, 46). As noted in its Indo-Pacific Strategy, it is crucial for the US to “encourage our allies and partners to strengthen their ties with one another, particularly Japan and the ROK” (White House 2022a, 9). The US has tried to handle South Korea–Japan problems mainly via its respective bilateral alliances with South Korea and Japan.

The US–South Korea and the US–Japan alliances began as asymmetric alliances in which a major, relatively stronger power formed with a relatively lesser power (Morrow Reference Morrow1991). A lesser power—in terms of military capabilities, often called a protégé—would gain enhanced security from a stronger power, or a patron. In return, the lesser power's autonomy would be compromised in favor of the stronger power, while the stronger power “gains autonomy—freedom of action—at some costs to its security” (Morrow Reference Morrow2006, 3). As the patron and stronger power, the US has provided enhanced security and gained a certain degree of leverage from South Korea and Japan while South Korea and Japan have compromised their autonomy to some degree in coordinating their policies with the US via the alliances.

A state's capabilities can change over time, and changes in relative capabilities within an asymmetric alliance can cause a transformation or evolution of the alliance (Park and Chun Reference Park and Chun2015). When a once lesser power has gone through significant political and economic development, it becomes more powerful than before and capable of taking a greater role with its strengthened military capability and material power (Heo and Roehrig Reference Heo and Roehrig2018). Despite its increased capabilities, it is often the case that the lesser power would still be relatively weaker than the patron and therefore have little intention to suspend or break its alliance with the stronger power due to continuously provided enhanced security benefits. Instead, with its increased capabilities and elevated status, the lesser power would more likely to “increase its autonomy without decreasing its security” (Park and Chun Reference Park and Chun2015, 41), revisiting the dynamics between itself and the stronger power.

Changes in states’ relative capabilities apply to the both the US–South Korea and US–Japan alliances. Compared to those early years when South Korea and Japan formed their alliances with the US, South Korea and Japan have achieved significant political, economic, and military development. South Korea and Japan were ranked the ninth and tenth of the top 15 military spenders in 2022.Footnote ⁷ Japan and South Korea were recorded as the third and thirteenth in the World Bank's Gross Domestic Product (GDP) ranking in 2022.Footnote ⁸ The US is the major power, without question, and meaningful gaps still exist between the US, South Korea, and Japan with respect to relative capabilities and material power. Though the gaps between the US and South Korea and Japan have become narrower, and the US has become more cooperative with South Korea and Japan, instead of unilaterally demanding their sacrifice or limiting their autonomy. Chun (Reference Chun2000, 83) describes such changes in the US–South Korea alliance as a “process of acquiring more autonomy for South Korea.” Similarly, Kim (Reference Kim2020, 28–29) describes the case of the defense cost sharing issue between the US and South Korea as “a patron–client relationship to be transformed into a partner relationship within an asymmetric alliance.”

The above discussion provides us with two seemingly competing but actually coherent possibilities for the US in handling of South Korea–Japan problems. In general, considering changes in relative capabilities, along with their increasing roles and influence in regional security, the US would more likely respect its allies’ autonomy and thus be less likely to involve itself in South Korea–Japan bilateral tensions. As long as the South Korea–Japan spat remains within their domestic politics and bilateral realms, thus projecting little impact on US interests and security, the US would have little reason to intervene and unnecessarily provoke its two crucial allies. On the other hand, if the US perceived that South Korea–Japan disputes were posing significant and negative consequences for its own national security interests, we would expect the US to intervene in South Korea–Japan problems. Given the existing, continued nature of asymmetry in the alliances, the US would be still capable of asking South Korea and Japan to reconsider and even change their policies in its own favor as the stronger, patron state. In other words, if South Korea–Japan disputes incur risks to the US and generate significant costs in terms of critical US national security interests, the US would be expected to use its leverage over South Korea and Japan to protect its national security interests. Thus, we argue that the US intervenes in South Korea–Japan tensions mainly when US critical national security interests are considered to be negatively affected; in all other cases, the US is less likely to intervene in the tensions and let the two allies deal with their bilateral tensions themselves.

In the next sections, we conduct granular examinations to evaluate our argument about the US involvement in South Korea–Japan disputes. First, by reviewing issues discussed in interactions among the US, South Korea, and Japan, we examine what constitutes US critical security interests and over what issues the US would be willing to consider intervening in South Korea–Japan problems to protect its critical security interests. Second, we conduct in-depth analysis on two competing situations, one with less involvement and the other with more involvement by the US in South Korea–Japan bilateral relations. Third, we provide qualitative interviews with former US government and military officials that we conducted from 2022 to 2024 to further confirm under what conditions the US is and is not willing to intervene in South Korea–Japan relations.

US national security interests with South Korea and Japan

We expect the US to be more likely and willing to intervene in South Korea–Japan disputes when it perceives intrusive and significant risks to its national security interests. The very first step to take to properly examine our argument is to determine what constitutes critical US national security interests with regard to South Korea and Japan, and more specifically, which issues the US is more concerned about with regard to South Korea and Japan. One way to adjudicate between different weights among various issues is to see which issues have been discussed most as a primary focus of US security interests via its relationship with South Korea and Japan. The more frequently the US mentions and refers to an issue, the more important and critical it is to US national security interests.

By exploring various official documents issued and released by the US governments in recent years, we found that North Korea is the most frequently discussed and significantly weighted issue in US national security interests in regard to its relationships with South Korea and Japan. More specifically, to address North Korean provocation via its nuclear and missile program and to pursue the denuclearization of the Korean Peninsula are the two most emphasized issues over which the US has constantly promised its commitments via its alliances with South Korea and Japan respectively and in terms of regional security. The Phnom Penh Statement between the leaders of the US, South Korea, and Japan cites North Korea as the very first task in securing the Indo-Pacific and beyond (White House 2022b). The denuclearization of the Korean Peninsula and deterrence of North Korean threats have been repeatedly mentioned in various US security documents, including the 2022 Indo-Pacific Strategy (White House 2022a), Interim National Security Strategic Guidance (White House 2021), the 2019 Indo-Pacific Strategy Report (US Department of Defense 2019), and the National Security Strategy documents of 2017, 2015, and 2010 (White House, 2017, 2015, 2010).

The US–South Korea alliance is “the linchpin of peace and prosperity in Northeast Asia, as well as the Korean Peninsula” and the US and South Korea “remain committed to the final, fully verified denuclearization of North Korea and enduring peace on the Korean Peninsula” (US Department of Defense 2019, 24–25). The US–Japan alliance is “the cornerstone of peace and prosperity in the Indo-Pacific” (US Department of Defense 2019, 22) in general, and in particular with respect to Northeast Asia and the Korean Peninsula, the US “continue[s] to work with Japan … deepening American, Japanese, and South Korean trilateral cooperation in the face of North Korea's dangerous and unlawful nuclear and ballistic missile program” (US Department of State 2021). The US has emphasized the importance of the US–South Korea–Japan trilateral cooperation and close coordination in recent years, most often in relation to North Korean threats. The Indo-Pacific Strategy (White House 2022a, 17) emphasizes US efforts of “strengthening extended deterrence and coordination with the ROK and Japan to respond to DPRK provocations, remaining prepared to deter—and, if necessary, defeat—any aggression to the United States and our allies.” The Interim National Security Strategic Guidance states: “We [the US] will empower our diplomats to work to reduce the threat posed by North Korea's growing nuclear and missile programs, standing shoulder-to-shoulder with the Republic of Korea and Japan” (White House 2021).

Having North Korea as a key issue in its national security interests, the US has to maintain closely coordinated and cooperative relations among South Korea, Japan, and the US to effectively handle North Korean challenges. If South Korea–Japan relations were to harm overall bilateral and trilateral channels for addressing North Korean issues, this would pose intrusive and prominent risks to US national security interests, incurring potentially significant costs for the US to pay. A recent Congressional Report (2023) made this point very clear: “a poor relationship between Seoul and Tokyo jeopardizes US interests by complicating trilateral cooperation on North Korea policy” (Congressional Research Service 2023, 25). In sum, considering its major power and ‘patron’ status in its bilateral alliances with South Korea and Japan individually, we expect the US to be more likely and willing to involve itself in South Korea–Japan relations to effectively manage security channels between its two closest Indo-Pacific allies, and as a result to successfully maintain its capability to deter North Korean threats.

We next delved into issues that were discussed bilaterally and trilaterally across South Korea, Japan, and the US—most importantly, which issues at the bilateral level prompted a US response or intervention into bilateral relations between Japan and South Korea. We constructed an original dataset on all issues discussed during interactions between South Korea and Japan bilaterally as well as with the US trilaterally, and US responses to issues discussed in interstate interactions, during the period from January 1, 2012 to August 31, 2023.Footnote ⁹ We used three specific event chronologies—US–South Korea, US–Japan, and South Korea–Japan—from “Comparative Connections”, produced by Pacific Forum as the main source for our data, with additional information collected using various news media and reports.Footnote ¹⁰ From January 1, 2012 to August 31, 2023, there were a total of 589 interactions,Footnote ¹¹ each of which involved one or more issues discussed between South Korea, Japan, and the US bilaterally or trilaterally. Of these total 589 interactions, 478, or 81.15 per cent, were bilateral between South Korea and Japan, with the remaining 111 interactions, or 18.85 per cent, trilateral interactions between South Korea, Japan, and the US.Footnote ¹² A total of 57 specific issues, all categorized under 13 general issues, were mentioned and discussed in interactions among South Korea, Japan, and the US bilaterally or trilaterally during the time frame, with a total of 817 frequencies for all issues discussed. This is presented in Table A2 in Appendix.

By examining our data on the issues discussed during interactions between the three states, we found that the issue of North Korea, among a total 13 general issues discussed, was the most frequently discussed one in general, accounting for 211, or 25.83 per cent, of the total 817 frequency of all issues discussed among South Korea, Japan, and the US.Footnote ¹³ When looking at trilateral interactions between South Korea, Japan, and the US, the issue of North Korea is the most discussed issue as well, with a much higher frequency: 113 times, or 58.25 per cent, of the total 194 frequencies of the issues discussed trilaterally throughout the entire time frame of the data.Footnote ¹⁴ Figure 1 shows that the issue of North Korea is the most discussed issue across three different US administrations—Obama, Trump, and Biden—during the entire temporal span of the data. Interesting to note is that neither historical issues nor maritime issues of South Korea–Japan disputes were discussed at trilateral interactions with the US. Those issues only relevant to South Korea–Japan bilateral relationsFootnote ¹⁵ were also not discussed in trilateral interactions with the US. This finding supports our argument that the US in general would not want to bring South Korea–Japan problems into a trilateral interaction as long as South Korea–Japan bilateral disputes stay within their own bilateral contexts and do not incur any harm to the US. Trilateral interactions among South Korea, Japan, and the US discussed general issues like North Korea, South Korea–Japan–US trilateral cooperation, global issues, China, and the GSOMIA, all of which the US has consistently confirmed as US priorities in strengthening the trilateral partnership.

Figure 1. List of issues discussed at the US–South Korea–Japan trilateral level, by each US administration, January 2012–August 2023

Note: (1) Obama administration years: January 2012–December 2016; Trump administration years: January 2017–December 2020; Biden administration years: January 2021–August2023. (2) The GSOMIA and Fukushima incidences were discussed once each under the Biden administration, but in neither the Obama nor Trump administration, thus these issues are not included in the figure.

In terms of US responses and interventions in South Korea–Japan bilateral relations and issues, the US intervened in only 21 out of 478 Japan–South Korea bilateral interactions, only 4.39 percent, over 7 issues with a total 31 out of a total 623 frequencies (4.98 percent). Not surprisingly, the issue of North Korea is the one that was most frequently discussed bilaterally between South Korea and Japan and led to a US reaction, 11 times out of a total of 31, or 35.48 percent, in frequency.Footnote ¹⁶ As shown in Figure 2, among the issues that were discussed bilaterally between South Korea and Japan across all three administrations, the issue of North Korea is the one that the US responded to most often, with the issue of ROK–Japan bilateral relationship receiving the second most frequent responses. The US has consistently emphasized a well-managed and closely coordinated relationship between South Korea and Japan for the sake of effective deterrence of North Korea. In that sense, when considering the issue of ROK–Japan bilateral relationship and the issue of North Korea altogether, North Korea is certainly the issue that the US most reacted to and thus cared about in terms of US national security and in pursuit of its trilateral partnership with South Korea and Japan. Another important point to note is that, in a few cases, mostly during the Obama administration (6 times) and once in the Biden administration, the US reacted to bilateral ROK–Japan historical disputes. Such findings appear to be against our expectation, but when looked at more closely, they do not contradict our argument. During the Obama administration, there was relatively increased attention to historical issues like comfort women, and some US politicians made comments about Japan's historical activities.Footnote ¹⁷ Yet, it is more important to note that the US reacted to South Korea–Japan bilateral historical disputes because it was concerned about South Korea–Japan relations with respect to its national interests. For instance, in December 2015, then National Security Advisor Susan E. Rice welcomed the South Korea–Japan agreement on comfort women, saying: “We[the US] look forward to deepening our work with both nations on a wide range of regional and global issues, on the basis of mutual interests and shared values, as well as to advancing trilateral security cooperation.”Footnote ¹⁸ In 2023, the Biden administration welcomed South Korea and Japan working together regarding wartime labor compensation, saying “a groundbreaking new chapter of cooperation and partnership between two of the United States’ closest allies.”Footnote ¹⁹

Figure 2. Issues discussed between ROK and Japan bilaterally and led to US responses, by each US administration, January 2012–August 2023

Note: Obama administration years: January 2012–December 2016; Trump administration years: January 2017–December 2020; Biden administration years: January 2021–August2023.

Our analysis, produces two interesting and coherent findings. First, the critical US national security interest of deterring North Korea is likely to provoke a response from the US and a willingness to intervene in South Korea–Japan bilateral relations. This suggests that if a South Korea–Japan spat had the potential to significantly damage US ability to address North Korean threats, and as a result disturb critical US national security interests, the US would be more likely and willing to consider intervening in South Korea–Japan bilateral relations. In these situations, the US would have sufficient reason to consider using its leverage, as the patron of the evolving but still asymmetric alliances with South Korea and Japan, to ‘make things right’ between South Korea and Japan for the benefit of US security interests. Second, even when the US seemed to get involved in issues that were solely bilateral issues between South Korea and Japan, it was mostly driven by US perceptions about potentially negative impacts these disputes might have on US capabilities to protect its own interests. As discussed above, US responses to South Korea–Japan historical issues of contention, discussed bilaterally though leading to US reactions, were mainly because the US saw potential costs of the bilateral tensions in terms of trilateral cooperation related to security interests.

Secured interests and US ‘stay-away’ in South Korea–Japan relations

Despite recurrent and ongoing tensions between South Korea and Japan, most of the US reactions to South Korea–Japan disputes have remained in a very diplomatic and rhetorical realm, without any tangible or direct actions or pressures upon South Korea and Japan. For instance, after the talks between Wendy Sherman, US Deputy Secretary of State, and Mori Takeo, Japanese Vice Minister for Foreign Affairs, in July 2021, Ned Price, spokesman for the US Department of State, commented: “We [the US] have long encouraged the ROK and Japan to work together on history-related issues in a way that promote healing and reconciliation … Even while addressing sensitive historical questions, cooperation on our common regional and international priorities must proceed.”Footnote ²⁰ Similarly, Assistant Secretary of State for East Asia and Pacific Affairs David Stillwell noted in July 2019, when tensions between South Korea and Japan arose (but before the GSOMIA incident): “the US won't seek to mediate the South Korea–Japan dispute, encouraging both to focus on key regional issues, including North Korea.” (US–Korea Chronology, Comparative Connections).

A major reason behind less US direct intervention in South Korea–Japan bilateral problems is that, in most cases, the US has perceived no direct and significant negative impact on its capability to address Noth Korean threats. Given North Korea's growing provocations and aggression in its missile and nuclear programs, the US has prioritized securing its military capabilities to deter North Korea and protect its national security interests via its alliances with South Korea and Japan in the region. In other words, even though South Korea and Japan are in disputes over contested issues, when it would not hurt US capabilities to maintain effective and efficient military cooperation and coordination between the three states to address security challenges by North Korea, the US would be less motivated to intervene in South Korea–Japan relations. Instead of poking the hornet's nest, it would be a much more logical and reasonable behavior for the US to remain an observer rather than intervene.

To further assess our argument, we reviewed political and diplomatic interactions that occurred between the US, South Korea, and Japan in the temporal span of 2018 to 2022, a particularly difficult time in South Korea–Japan relations, using event chronologies of interactions between the US and South Korea and the US and Japan, and the three states trilaterally from “Comparative Connections” produced by the Pacific Forum, as well as information from the US Department of State. A US Congressional report (2023, 5) noted that “beginning in 2018, a series of actions and retaliatory countermeasures by both governments involving trade, security, and history-related controversies caused South Korea–Japan relations to plummet, eroding US–South Korea–Japan policy coordination.” Events to be noted in this period cover major contentious issues between South Korea and Japan, including South Korea's court rulings about wartime labor and compensations by Japanese companies; trade disputes over the white list between South Korea and Japan related to historical grievances over comfort women; and the General Security of Military Information Agreement (GSOMIA) incident in which South Korea threatened to pull out of the information-sharing pact. This 2018–2022 period also covers changes in administrations in both South Korea and Japan—Moon Jae-in and Yoon Suk-yeol administrations in South Korea, as well as three prime ministers in Japan—Shinzo Abe, Yoshihide Suga, and Fumio Kishida. In this sense, we believe this short but complex five-year temporal span is an ideal period to further evaluate how the US would perceive South Korea–Japan relations in terms of its national security interests and decide whether to intervene or not.

We found that, despite ongoing tensions between South Korea and Japan, the three states—South Korea, Japan, and the US—continued to meet trilaterally, a total of 58 times from 2018 to 2022, to address security threats by North Korea.Footnote ²¹ Trilateral meetings between South Korea, Japan, and the US to discuss the issue of North Korea neither ceased nor were blocked due to South Korea–Japan tensions. For instance, in August 2019, the US, South Korea, and Japan held a trilateral meeting in Thailand during the ASEAN-related meetings, in the midst of increasing South Korea–Japan tensions over the GSOMIA. Since South Korea–Japan tensions have not disrupted joint efforts to address North Korean security threats, the US has had a tendency to minimize its direct involvement in South Korea–Japan disputes and has rather distanced itself from their own problems. When considering increasing roles by South Korea and Japan to deal with North Korean issues, particularly along with both states’ increasing capabilities and elevated global status, the US has less reason to provoke either ally by unnecessarily intervening, thus limiting their autonomy over their own historical and territorial disputes. The continued and regular trilateral meetings to address the North Korea problem indicate that the US has not had to intervene in bilateral issues very much in order to get Japan and South Korea to work together with the US to effectively deter North Korea.

Interviews with former US government and military officials support our argument and findings on the overall US position toward South Korea–Japan relations. Interviewees collectively admitted that the US well recognizes hostile relations between South Korea and Japan over their contested historical and territorial issues, therefore treating these tensions as a default condition in planning US strategy. Admiral Harry B. Harris, USN (Ret.), former US Ambassador to the Republic of Korea and former Commander of the US Pacific Command, noted: “We've [the US] developed a strategy, recognizing that there's a challenge between them [Japan and South Korea]. It's not like we have a strategy that assumes that Japan and South Korea are going to get along. In fact, it doesn't make that assumption, and the strategy recognizes that that they don't get along.”Footnote ²² Similarly, a high-ranking retired US military officer and diplomat noted the importance of trilateral coordination to US security: “It is crucial for the three nations to work together to enhance security cooperation and preserve the international rules-based order. Notwithstanding the current tensions between Seoul and Tokyo—and these are not insignificant—the reality is that no important security or economic issue in the region can be addressed without both South Korea's and Japan's active involvement.”Footnote ²³

As the US is fully aware of long-standing contentious relations between South Korea and Japan that are hard to resolve, the US has in general maintained a neutral position of not getting involved in South Korea–Japan spat tensions, simply pursuing trilateral channels to address security challenges crucial to US national interests and shared security interests. Lieutenant General Wallace Gregson, USMC (Ret.), former Commanding General of Marine Corps Forces Pacific and Marine Corps Forces Central Command, and former Commanding General of III Marine Expeditionary Force in Japan, made this point clear in an interview:

Lieutenant General, USMC (Ret.) Lawrence Nicholson, former Commanding General of III Marine Expeditionary Force in the Asia-Pacific region, also made a similar point, saying:

Some interviewees pointed out possible backlash that the US involvement could bring out as a very undesirable outcome for the US with respect to South Korea–Japan problems. From such perspective, interviewees re-addressed the strategic necessity of the US being neutral between its two important allies and thus pursuing a ‘stay-away’ strategy regarding South Korea–Japan disputes. David Stillwell, former Assistant Secretary of East Asian and Pacific Affairs noted: “Our [the US] going in position is to let them work it out themselves. Like a domestic dispute, trying to break up the fight almost always ends up with the peacekeeper getting the worst of it.”Footnote ²⁶ James Schoff, former Senior Adviser for East Asia policy at the US Office of the Secretary of Defense, noted the same US strategy toward South Korea–Japan relations: “The US encourages both sides to overcome historical issues for the sake of shared strategic interests, but it doesn't try to mediate or pass judgement on one side's view over the other.”Footnote ²⁷

Threatened interests and US ‘involvement’ in South Korea–Japan relations

During her interview, Yuki Tatsumi, Director of the Japan Program at the Stimson Center, provided insight into when the US would get into South Korea–Japan relations:

This statement clearly chimes with our argument that the US is more likely and willing to consider using its leverage toward South Korea and Japan when it perceives potential risks and threats to its critical national security interests caused by South Korea–Japan disputes. In this section, we explore two related incidents in which the US intervened in South Korea–Japan disputes when it perceived possible harm to its security interests, both from 2019: the South Korea–Japan trade dispute over Japan's white list and the South Korea–Japan spat over the GSOMIA. In response, the US pressured Japan and South Korea to rethink their positions as the disputes increasingly affected US national security concerns about North Korean threats.

In November 2018, the South Korean Supreme Court ruled to order Japanese companies to pay individual compensations to South Korean victims of wartime forced labor.Footnote ²⁹ Japan instantly responded with great disappointment and dissatisfaction toward South Korea, arguing that it was a violation of the 1965 treaty that resolved all compensation-related issues between South Korea and Japan.Footnote ³⁰ Together with the court ruling and a contention in December 2018 over a South Korean navy ship pointing its radar at a Japanese military aircraft, the South Korea–Japan bilateral relationship was frozen. On July 1, 2019, Japan's Ministry of Economy, Trade, and Industry announced export restrictions on the export and transfer of controlled items and their relevant technologies to South Korea.Footnote ³¹ Initially, US president Donald Trump showed a reluctance but also a potential willingness to get involved in the South Korea–Japan dispute, saying: “maybe if they would both want me to, I'll be. It's like a full-time job getting involved with Japan and South Korea.”Footnote ³² The US did not fully disregard the South Korea–Japan trade dispute, but instead, it tried to manage the economic dispute, mainly because the deteriorating relationship between Japan and South Korea “puts US strategic objectives at risk” (Klinger and Walters Reference Klingner and Walters2019) and “endanger[s] sustained US efforts on North Korea.”Footnote ³³ This position indicates that US involvement was very likely due to strategic interests rather than merely wanting to help the two US allies resolve the dispute over Japan's white list.

Still, the US reaction remained mostly as strong ‘encouragement,’ instead of direct involvement in the South Korea–Japan dispute until July 2019. In an interview, James Schoff recalled the situation then:

David Stilwell, then US Assistant Secretary of State for East Asian and Pacific Affairs, commented that “Washington encouraged its two friends to resolve the issue through dialogue.”Footnote ³⁵ US Secretary of State Mike Pompeo also called for a “standstill agreement” between Japan and South Korea given the increasing trade disputes and tensions between two states, but without significant pressure.Footnote ³⁶

The situation changed dramatically when the South Korean government dragged the GSOMIA into the dispute. The GSOMIA, an information sharing pact, was signed on November 23, 2016 between South Korea and Japan to facilitate seamless and effective intelligence sharing between South Korea and Japan (and the US) regarding North Korean missiles and North Korean activities in the region.Footnote ³⁷ Secretary of Defense Ash Carter welcomed the agreement, stating that: “The ROK–Japan GSOMIA will enable increased information sharing and strengthen cooperation between our two closest allies in Northeast Asia.”Footnote ³⁸ General Vincent K. Brooks, Combined Forces Command and US Forces Korean Commander, also commented: “This agreement will promote greater collaboration and enhance the readiness of the combined ROK and US forces to respond to the unacceptable threat posed by North Korea.”Footnote ³⁹

On August 22, 2019, as a counter-measure against Japan's removal of South Korea from its Whitelist, the South Korean government announced that it would not renew the GSOMIA with Japan. Given further intensifying economic and historical disputes between South Korea and Japan, the Moon administration reiterated its willingness to withdraw from the GSOMIA in November 2019. South Korea's refusal to renew the GSOMIA was instantly and certainly perceived by the US as directly and negatively impacting its ability to deter North Korean threats, as the information sharing system, which had helped maintain security for the three states and the region, was about to end. As a result, the US put unprecedented pressure directly on South Korea to overturn its policy regarding the GSOMIA. Pentagon spokesman Lt. Col. Dave Eastburn commented: “The Department of Defense expresses our strong concern and disappointment that the Moon administration has withheld its renewal of the Republic of Korea's General Security of Military Information Agreement with Japan.”Footnote ⁴⁰ US Department of State spokesperson delivered unusually rare, blunt, and public criticism of South Korea's decision to pull out of the GSOMIA: “We are deeply disappointed and concerned that the ROK's government terminated the General Security of Military Information Agreement (GSOMIA) … This will make defending Korea more complicated and increase risks to US forces.”Footnote ⁴¹ Assistant Secretary of Defense for Indo-Pacific Security Affairs Randall Schriver stated: “Historical disputes, animosities and political disagreements should be kept separate from shared vital military and security cooperation.”Footnote ⁴² Secretary of Defense Mark Esper and Chairman of the Joint Chiefs of Staff General Joseph Dunford Jr. similarly shared their grievances and disappointment toward South Korea's decision of withdrawing from the GSOMIA at the Department of Defense Press Briefing.Footnote ⁴³

In November 2019, after much pressure from the US, South Korea backed away from scrapping the GSOMIA and announced that it would retain the GSOMIA with Japan. The US State Department welcomed the South Korean decision, saying: “Given our shared regional and global challenges, decisions to strengthen trilateral cooperation are timely and critical.”Footnote ⁴⁴ This overturn of South Korea's decision—a direct example of a government giving up its policy autonomy due to a stronger ally's pressure—clearly demonstrates that pressure from the US was significant enough for South Korea to compromise its autonomy in favor of the US. It is also a clear signal that the US was willing to get involved in South Korea–Japan problems when it perceived significant threats to its critical security interests and potential harm to its capability to address primary security challenges—North Korea. The 2020 Asia-Pacific Regional Security Assessment summarizes how influential the intensive and blunt US pressure on South Korea was in the GSOMIA incident: “In late November 2019, strong pressure from Washington resulted in Seoul reversing its August decision to pull out of the bilateral General Security of Military Information Agreement (GSOMIA) with Japan (46) …Washington has sought to intensify cooperation with South Korea and Japan in order to help manage the threat posed by North Korea, and even longer term, China (94)” (Asia-Pacific Regional Security Assessment 2020).

David Stilwell indicated in his interview how risky it would have been for the GSOMIA to lapse: “When their [South Korea and Japan] failure to cooperate puts American lives at risk: 22,500 US forces plus families on the peninsula and 50,000 plus families, 100,000 plus, in Japan. The Moon administration's reluctance to share important missile tracking information was unacceptable. [And] When that friction is allowed to undermine the others’ interests in the region. [the US would intervene in South Korean–Japanese relations and pressure one or both government]”Footnote ⁴⁵ Harry Harris similarly recalled the GSOMIA incident in his interview: “GSOMIA affected our [the US] ability … and it actually put Americans at risk, Americans in Korea and in Japan at risk. … the GSOMIA doesn't affect just the Korean Peninsula; it's not geographically limited. The previous agreement, the trilateral thing had a geographic boundary. But the GSOMIA was unbounded.”Footnote ⁴⁶ Yuki Tatsumi also noted how much the US cared about its own, as well as trilateral capabilities to effectively deter North Korean threats via the GSOMIA: “Information needs to flow seamlessly among the three [states], so that was another reason the US side thought GSOMIA was very, very important. … something like GSOMIA, if it falls apart—a lot of security-side cooperation or defense-side cooperation is contingent on if the GSOMIA exists—at least that is how the US was envisioning it. So, that is why in that particular instance, it did lean in more heavily because they needed that GSOMIA to start working, and it was problematic when South Korea started to and continued to refuse to come back on implementing it.”Footnote ⁴⁷