Japan-Korea: Working Together as Like-Minded Countries?

Por ISOZAKI Atsuhito — The Diplomat

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Japan and South Korea share more than enough to work together on North Korea — but less than is often assumed.

Japanese Prime Minister Takaichi Sanae and South Korean President Lee Jae-myung attend a summit meeting in Andong, South Korea, May 19, 2026.

It is frequently argued that “Japan and South Korea are like-minded countries who share values and ought to strengthen their cooperation in dealing with North Korea.” The question worth asking is what the two countries are actually “like-minded” about — and what they are not.

There is no settled definition in international politics of “like-minded countries” — a concept increasingly prominent in Japanese diplomatic discourse as dōshikoku —, but the term generally refers to countries that share objectives or an understanding on specific issues. The two countries are not automatically like-minded simply because they are both democracies, nor do their policies automatically align across diverse fields because they are both U.S. allies. The degree of alignment has to be assessed issue by issue.

Japan-South Korea relations on the North Korean issue do have an evident duality. On the “threat” dimension, the two are quite robustly like-minded: both are concerned about North Korea’s growing nuclear and missile capabilities, and there is considerable room for cooperation in countering cyberattacks and cryptocurrency theft. The importance of Japan-South Korea security cooperation is also growing as the Russia-North Korea military relationship deepens. In managing relations with an unpredictable U.S. president, too, the bilateral Japan-South Korea framework has become if anything more important than the broader trilateral one.

The differences become apparent, however, the moment North Korea is treated not as a “threat” but as a potential “negotiation partner.” In South Korean eyes, North Korea is simultaneously a military threat and one half of a divided nation sharing a common language. Depending on the administration, the emphasis varies, but Seoul can never entirely set aside the questions of peaceful coexistence and eventual reunification.

Japan, by contrast, regards North Korea as a foreign country across the sea. Drones do not fly over from North Korea to Japan as they do to South Korea, and Japan’s North Korea policy is heavily constrained by the abduction issue — a factor absent for every other country in the region. Even if progress were made on nuclear and missile issues, it would be politically impossible for Tokyo to move toward normalization without meaningful progress on abductions.

Even if both Tokyo and Seoul were to support “dialogue” and “diplomacy” with Pyongyang, the underlying expectations would differ. Seoul values dialogue that eases inter-Korean tensions; Tokyo requires dialogue that advances its outstanding issues with Pyongyang. Even on denuclearization, where the ultimate goal may appear aligned, the two sides diverge over whether to treat a freeze of North Korea’s nuclear capabilities as an intermediate  milestone, and over when sanctions should be eased — Japan still insisting on CVID (complete, verifiable, irreversible denuclearization).

And then there is the Chinese variable. It is difficult to consider the efficacy of sanctions or future diplomatic negotiations without involving China, North Korea’s foremost economic partner. Yet Japan and South Korea often view China quite differently. Japan perceives China primarily as a long-term security threat, while South Korea sees it as both a concern and an indispensable partner for managing the Korean Peninsula. Even conservative South Korean presidents have at times prioritized ties with Beijing over alignment with Tokyo. The geopolitical weight of sharing a land border with China is not something Seoul can ignore.

These differences, however, hardly make cooperation impossible. On the contrary, the right approach is to treat cooperation as necessary precisely because interests and priorities diverge. If U.S. President Donald Trump were to pursue a summit with North Korean leader Kim Jong Un for legacy purposes, both Japan and South Korea would seek to resume negotiations with Pyongyang in some form, each naturally prioritizing its own interests. History shows repeated failures to act in concert, each time expanding North Korea’s room for maneuver. Pyongyang has always sought to drive a wedge between Tokyo and Seoul, and between the two of them and Washington.

Japan-South Korea cooperation on North Korea need not aim for complete policy alignment. Japan should pursue its own diplomacy with Pyongyang; South Korea should occupy its own space in inter-Korean relations. On that foundation, the two should share information closely and keep each other fully informed of what each prioritizes and where neither can compromise. The same applies to China: a shared understanding of when Beijing should be treated as a partner and when it should be viewed with caution. On issues of this kind, diplomatic channels matter more than defense channels.

Japan and South Korea will never adopt identical policies toward North Korea — nor should they need to. That does not mean they cannot be like-minded countries. The real question is whether they can manage their differences on North Korea and China with sufficient steadiness and dexterity. That capacity, more than any policy alignment, is what will determine whether the “like-minded” label truly fits.

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It is frequently argued that “Japan and South Korea are like-minded countries who share values and ought to strengthen their cooperation in dealing with North Korea.” The question worth asking is what the two countries are actually “like-minded” about — and what they are not.

There is no settled definition in international politics of “like-minded countries” — a concept increasingly prominent in Japanese diplomatic discourse as dōshikoku —, but the term generally refers to countries that share objectives or an understanding on specific issues. The two countries are not automatically like-minded simply because they are both democracies, nor do their policies automatically align across diverse fields because they are both U.S. allies. The degree of alignment has to be assessed issue by issue.

Japan-South Korea relations on the North Korean issue do have an evident duality. On the “threat” dimension, the two are quite robustly like-minded: both are concerned about North Korea’s growing nuclear and missile capabilities, and there is considerable room for cooperation in countering cyberattacks and cryptocurrency theft. The importance of Japan-South Korea security cooperation is also growing as the Russia-North Korea military relationship deepens. In managing relations with an unpredictable U.S. president, too, the bilateral Japan-South Korea framework has become if anything more important than the broader trilateral one.

The differences become apparent, however, the moment North Korea is treated not as a “threat” but as a potential “negotiation partner.” In South Korean eyes, North Korea is simultaneously a military threat and one half of a divided nation sharing a common language. Depending on the administration, the emphasis varies, but Seoul can never entirely set aside the questions of peaceful coexistence and eventual reunification.

Japan, by contrast, regards North Korea as a foreign country across the sea. Drones do not fly over from North Korea to Japan as they do to South Korea, and Japan’s North Korea policy is heavily constrained by the abduction issue — a factor absent for every other country in the region. Even if progress were made on nuclear and missile issues, it would be politically impossible for Tokyo to move toward normalization without meaningful progress on abductions.

Even if both Tokyo and Seoul were to support “dialogue” and “diplomacy” with Pyongyang, the underlying expectations would differ. Seoul values dialogue that eases inter-Korean tensions; Tokyo requires dialogue that advances its outstanding issues with Pyongyang. Even on denuclearization, where the ultimate goal may appear aligned, the two sides diverge over whether to treat a freeze of North Korea’s nuclear capabilities as an intermediate  milestone, and over when sanctions should be eased — Japan still insisting on CVID (complete, verifiable, irreversible denuclearization).

And then there is the Chinese variable. It is difficult to consider the efficacy of sanctions or future diplomatic negotiations without involving China, North Korea’s foremost economic partner. Yet Japan and South Korea often view China quite differently. Japan perceives China primarily as a long-term security threat, while South Korea sees it as both a concern and an indispensable partner for managing the Korean Peninsula. Even conservative South Korean presidents have at times prioritized ties with Beijing over alignment with Tokyo. The geopolitical weight of sharing a land border with China is not something Seoul can ignore.

These differences, however, hardly make cooperation impossible. On the contrary, the right approach is to treat cooperation as necessary precisely because interests and priorities diverge. If U.S. President Donald Trump were to pursue a summit with North Korean leader Kim Jong Un for legacy purposes, both Japan and South Korea would seek to resume negotiations with Pyongyang in some form, each naturally prioritizing its own interests. History shows repeated failures to act in concert, each time expanding North Korea’s room for maneuver. Pyongyang has always sought to drive a wedge between Tokyo and Seoul, and between the two of them and Washington.

Japan-South Korea cooperation on North Korea need not aim for complete policy alignment. Japan should pursue its own diplomacy with Pyongyang; South Korea should occupy its own space in inter-Korean relations. On that foundation, the two should share information closely and keep each other fully informed of what each prioritizes and where neither can compromise. The same applies to China: a shared understanding of when Beijing should be treated as a partner and when it should be viewed with caution. On issues of this kind, diplomatic channels matter more than defense channels.

Japan and South Korea will never adopt identical policies toward North Korea — nor should they need to. That does not mean they cannot be like-minded countries. The real question is whether they can manage their differences on North Korea and China with sufficient steadiness and dexterity. That capacity, more than any policy alignment, is what will determine whether the “like-minded” label truly fits.

ISOZAKI Atsuhito is a professor at Keio University.

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Fonte: The Diplomat