This past week, U.S. Secretary of State Antony Blinken and Secretary of Defense Lloyd Austin made back-to-back visits to Tokyo and Seoul, a move intended to bolster U.S. alliances in Asia and signal a united front toward a rising China. This early diplomatic foray is a welcome effort by the Biden administration to implement its coalition-based approach to the Indo-Pacific region. But its ultimate success in part turns on how well the United States can resolve the rifts between Japan and the Republic of Korea (ROK). To help overcome their differences, the United States must serve as a key convenor, seeking ways to deepen U.S.-Japan-ROK relations through addressing their shared challenges.

This essay proceeds as follows. First, we assess the current state of trilateral relations, discuss the drivers and constraints of trilateral cooperation, and outline the asymmetric advantages that trilateralism provides in general, and in Northeast Asia in particular. Finally, we identify emerging challenges and opportunities for further advancing trilateral cooperation.

State of Play: Trilateral Dissonance

Despite longstanding efforts by each nation, prospects for trilateral cooperation hit a low-water mark in 2019. For over three decades, Seoul and Tokyo have tussled over different interpretations of their 1965 Treaty on Basic Relations, which on its face absolved Japan of all its colonization-related debts. In 2018, however, the ROK Supreme Court ruled that, notwithstanding past agreements, Japanese companies had to make reparations for their past use of forced labor. Following this controversial ruling, tensions boiled over. Both nations removed the other from most-favored-nation trading status. Tokyo placed export restrictions on critical inputs for South Korea’s large semiconductor industry, among others, while Koreans organized nationwide boycotts on Japanese goods and businesses. The dispute culminated in Seoul’s near withdrawal from an important military intelligence-sharing pact with Tokyo. Bilateral relations did not improve in 2020, with reciprocal coronavirus travel restrictions, since lifted, reducing further opportunities for person-to-person engagement, an important anchor of public goodwill.

Last September, many in South Korea, including President Moon Jae-in, hoped that the election of Prime Minister Suga Yoshihide would provide an opportunity for renewed Japan-ROK relations. Current domestic politics in both nations, however, continue to limit Suga’s capacity to innovate far beyond the foreign policies of his predecessor. Meanwhile, the United States under President Donald Trump repeatedly second-guessed the value of U.S. alliances in Asia, curtailing Washington’s ability to assume its customary role as bridge-builder between Tokyo and Seoul. By the close of the Trump administration, prospects for trilateral cooperation appeared as bleak as ever in recent memory.

Recognizing the growing threats posed by China and North Korea, however, the Biden administration came into office seeking to rejuvenate trilateral cooperation. In recent weeks, Washington inked military cost-sharing deals with both Seoul and Tokyo, talks that had been stalled as the previous administration demanded premium costs for hosting U.S. troops. For his part, Moon struck a conciliatory tone with Japan during his latest March 1 national address, highlighting the importance of bilateral cooperation for “stability and common prosperity in Northeast Asia” alongside trilateral relations. To date, however, Tokyo has been relatively subdued in response, though the new Japanese envoy to South Korea publicly stated that Tokyo and Seoul were “mutually important neighbors.” And while the U.S. meetings this week elicited public statements in both Japan and South Korea on the importance of trilateralism, a resurgence of trilateral relations under Joe Biden remains far from inevitable.

Melting Pot: Geopolitics, Identity, and History

Indeed, the Biden administration faces a myriad of countervailing factors that limit deeper cooperation. The first is the geopolitical structure of Asia. As an island nation, Japan traditionally has sought the creation of an Asian security architecture that is multipolar, maritime, and beyond the historic sphere of Chinese continental influence. On the other hand, the Korean peninsula geographically adjoins China while sitting across a narrow strait from Japan. Koreans throughout history, therefore, have intuited the existential need to hedge between great powers.

Despite the tension underlying these divergent strategic logics, relations between Tokyo and Seoul have generally improved when they shared a common danger or a sense of insecurity. Indeed, they overcame their historical differences on multiple occasions during the Cold War when the United States threatened to withdraw its defense commitments from the region. For much of the past three decades, North Korea’s growing arsenal of ballistic missiles and nuclear weapons has provided ample motivation for alignment.

But a geopolitical assessment alone does not fully explain the current frosty relations between these two U.S. allies. When the Trump administration’s policies renewed questions of U.S. commitment to the region, the two nations should have been drawn closer, as they did on multiple past occasions. Yet, each side appeared unable to muster the requisite urgency for cooperation. Nor do South Korea’s deep economic ties to China sufficiently explain its relative openness to Beijing, because China remains Japan’s largest target market even as Tokyo has held Beijing at arm’s-length. Finally, while South Korea and Japan are close trading partners buttressed by considerable investment flows, these strong economic ties have not overcome nationalist sentiments. If anything, economic leverage has often been deployed as a tool of diplomatic warfare. When the ROK Supreme Court ruled against Japanese companies for reparations, Tokyo’s response was economic retaliation, which Seoul repaid in kind.

In addition, antithetical national identities rooted in history drive the two sides further apart. South Korea views itself as the survivor of Japanese imperialism, a mature democracy, and an independent middle-power in its own right. Japan also sees itself as a survivor of World War II, yet has had to reform to pacifism and prove itself a steward of democracy during the Cold War many times over. But Koreans doubt that Japan has truly transformed, a fundamental challenge to the Japanese people’s collective narrative. These differences are highlighted in the unresolved disputes over the ownership of the Dokdo/Takeshima islands, portrayals of Japan’s imperialism in Japanese textbooks, and the issue of comfort women and other forced labor reparations dating to Japanese colonialism. While each side’s national story may not be immutable, the two certainly are incompatible.

Finally, South Korea assesses its geopolitical situation through a historical lens. As scholars have noted, throughout history “China has been [South Korea’s] most persistent invader, but Japan was the most recent.” This reality seems to have made a lasting impression in South Korea. Since Korea’s decolonization in 1945, China has been a repeated aggressor against its neighbors. More recently, it has aggressively extended its territorial claims in the East and South China Seas and, in June 2020, engaged in a border standoff with India which led to dozens of casualties. Japan, meanwhile, remains under a pacifist constitution and has proceeded to securitize only incrementally, despite ongoing debates about revising the operative Article 9 provision. Yet it is Tokyo, not Beijing, that many South Koreans seem to instinctively fear of falling into militarism.

Trilateral Asymmetries

On balance, it appears the historical and identity forces propelling the trilateral partners farther apart are, for now, outweighing the geopolitical and economic factors that draw them closer together. Yet there are good reasons to try to strengthen the relationship. Trilateralism offers benefits unique from those available from unilateral, bilateral, or other multilateral approaches.

Trilateral relationships are formed for a simple reason: nations see a shared benefit that would be too costly or dangerous to pursue by other diplomatic means. Indeed, a trilateral approach provides political cover for the three nations to cooperate, where bilateral impediments between any two legs of the triangle could inhibit engagement. Moreover, trilateral frameworks can avoid some of the overly administrative and bureaucratic burdens in multilateral settings that unnecessarily slow down progress. Because of such advantages, there has been an explosion of such “minilaterals” in the past decade.

In the case of U.S.-Japan-South Korea trilateralism, each country stands to benefit from cooperating against North Korea, a threat that would be too costly for any one nation to defend against alone. Leaders in Tokyo and Seoul invariably set off political landmines when they seek to cooperate bilaterally, which is another possible reason why Moon and Suga have hesitated to recommence discussions without a third-party present like Washington or Beijing. As has been observed, joint military efforts between Japan and South Korea are generally able to avoid the usual public scrutiny if they are under the cover of trilateral coordination with the United States as the convener. Moreover, it is an underappreciated point that Seoul and Tokyo can increase their collective leverage over Washington by approaching with joint demands.

Trilateralism can also lead to unintended effects, however, such as opportunity costs, security dilemmas, and diplomatic breakdowns. To be sure, these risks are not unique to trilateralism; they exist just as well in any bilateral or multilateral context. Perhaps a risk unique to trilateral relations is that one weak leg of the triangle could infect relations between either of the other two legs. This has occurred on occasion in the U.S.-Japan-ROK context, for instance, when the United States intervened too assertively on one side or the other of ongoing historical disputes, leading to backlash charged by claims of favoritism.