The Quiet Progress of Military Cooperation between South Korea and Japan

Earlier this month, the United States, Japan, and South Korea concluded the fourth iteration of Freedom Edge, their trilateral military exercise. Compared to other developments in the region that attracted significant media attention, such as President Donald Trump’s decision to curtail military exercises with South Korea, this year’s trilateral exercise proceeded without much fanfare or reporting, and perhaps deliberately so.

Freedom Edge grew out of an initiative by former presidents Joe Biden and Yoon Suk Yeol, and former prime minister Kishida Fumio to deepen defense cooperation. The effort began with the sharing of real-time ballistic missile warning and tracking data in 2022 and a political commitment in 2023 for trilateral cooperation followed by the first-ever joint aerial exercise among the three countries. It then led to a 2024 agreement on a “multi-year plan” for institutionalizing cooperation and expanding the scope of exercises that began with Freedom Edge. The first iteration of Freedom Edge focused mostly on the maritime domain; it has since grown in scope and now “integrates air, maritime, missile defense, cyber, and medical capabilities in a more connected training environment.”

The endurance of the trilateral exercise is notable: it survived leadership changes in all three countries when many policy initiatives fade away with changes in administration. Moreover, direct defense cooperation between South Korea and Japan has never been the norm, even in a trilateral setting, due to historical sensitivities and disputes related to Japan’s colonial rule in Korea. Previous initiatives to promote cooperation between the two countries were often derailed even when the political leaders wanted to commit their countries to the path of closer cooperation.

For this reason, when the three sides agreed to institutionalize trilateral cooperation at Camp David in 2023, there were doubts about the sustainability of the commitment. The decision by the conservative Yoon administration to engage militarily with Japan drew criticism at the time from progressives in Korea, with many viewing his Japan policy as an unjust concession made to Japan. The trilateral military exercise also runs counter to the progressive agenda of pursuing dialogue with Pyongyang, which has reacted harshly and accused the exercise of being “offensive” and involving “nuclear elements.”

In the face of all this, it is remarkable that military cooperation is proceeding apace under the new progressive government in South Korea. Historical sensitivities remain salient in South Korea but have not so far significantly affected military cooperation with Japan. In 2026, efforts to hold those who collaborated with Japanese colonial rule accountable and recover their assets were revived in South Korean domestic politics. In August, the issue became a political controversy and reached the National Assembly—just two weeks before Freedom Edge was scheduled to commence.

Yet Freedom Edge proceeded quietly as planned, without noticeable opposition from politicians, media, or the public. Perhaps tellingly, in a speech given on Liberation Day, a public holiday marking the end of Japanese colonial rule, President Lee Jae-myung himself acknowledged the law that would re-establish the commission for confiscating assets associated with collaboration but at the same time stressed the importance of deepening ties with Japan.

What does this mean for trilateral military cooperation and the future of the bilateral relations? These developments suggest that, at least for now, there is a clear desire within the three capitals to continue existing frameworks for trilateral military cooperation, if necessary, by keeping cooperation low-key and less visible to the public. Despite Trump’s decision to curtail military exercises with Seoul, clearly, many in Washington view continuing trilateral cooperation as beneficial. South Korea and Japan are likely both driven by a shared desire to avoid weakening the U.S. commitment to the region and the unraveling of existing frameworks for cooperation. It also perhaps reflects a growing recognition that aligning strategic priorities among the three countries is necessary for maintaining their relationship with the United States.

The lack of politicization of military cooperation could also reflect shifting trends in South Korea-Japan relations. Favorable views of Japan among South Koreans are at a record high, and the two societies continue to develop closer cultural ties, while geopolitical uncertainties remain high. The desire to keep defense cooperation separate from other areas of disagreement and potentially explosive political issues is noteworthy. While these trends could be reversed, they do suggest that the political incentives to raise or escalate contentious issues in ways that disrupt military cooperation are lower than in previous years.

The degree of cooperation remains modest. There is still considerable caution regarding more direct and substantive bilateral cooperation, such as a logistics support agreement. Efforts to dramatically upgrade the relationship may even trigger domestic political backlash. It is also possible that trilateral cooperation could be undone by an unforeseen, politically explosive issue that brings latent disagreements and grievances to the fore.

But institutionalized cooperation, once established, tends to persist unless actively challenged. The trends suggest, at least in the near term, that all sides have an interest in sustaining the cooperation.

Jung Jae Kwon is a postdoctoral fellow in technology and international security at the UC Institute on Global Conflict and Cooperation (IGCC) in Washington, D.C.

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