Japan and South Korea Navigate a Turbulent World

Japanese Prime Minister Sanae Takaichi and South Korean President Lee Jae Myung held a summit on May 19, 2026 in Lee’s hometown of Andong. The meeting came shortly after U.S. President Donald Trump met President Xi Jinping on May 14-15. As was the case in January, when a China-South Korea summit was swiftly arranged at Beijing’s request just ahead of Takaichi’s previous meeting with Lee, both the Japanese and Korean governments are acutely aware of their shared challenge: managing the dynamics of a shifting U.S.-China relationship.

The central themes of the U.S.-China summit were Taiwan, Iran, and trade, with the Korean Peninsula a secondary concern. With Japan-China tensions over Taiwan running high, Japan followed the Trump-Xi summit more closely than South Korea did. In fact, immediately after the summit, on May 15, Takaichi was briefed by phone by Trump while he was still en route home, whereas Lee was not briefed until somewhat later, on May 17.

Japan and South Korea agree that countering China’s economic coercive diplomacy requires deepening their cooperation on economic security within the Japan-U.S.-South Korea framework, and that U.S. engagement is indispensable. There is, however, a difference in tone on China. Seoul wants to keep the U.S.-South Korea alliance from becoming entangled in the Taiwan issue, and to maintain workable relations with Beijing, mindful of the economic stakes and the North Korean problem. The gap was visible in the joint press announcement, where Lee referred to trilateral cooperation among Japan, China, and South Korea, while Takaichi referred only to the Japan-U.S.-South Korea framework. This divergence over China is one reason why the Acquisition and Cross-Servicing Agreement (ACSA) remains unresolved.

Both countries also face a common energy challenge: with 90 percent of their oil coming from the Middle East, Japan and South Korea must balance their U.S. alliance commitments against the need to avoid antagonizing Tehran. The summit produced concrete results on energy security, including an agreement on swap arrangements to mutually cover shortages of crude oil and LNG.

Washington has asked Japan, South Korea, and other allies to contribute naval forces to ensure safe passage through the Strait of Hormuz. Public opinion in both countries is largely critical, and both governments have been cautious. The situation remains fluid. Whether the conflict drags on or a ceasefire holds, if the Trump administration presses allies for greater burden-sharing, Japan and South Korea will face a difficult choice; acting in concert will be critical to avoid either country being penalized alone for its response. Close and continuous coordination between Tokyo and Seoul on this issue is essential.

Trump hopes to hold another summit with North Korean leader Kim Jong Un; the two last met during Trump’s first term in 2019. In Seoul, Lee also has high hopes for Trump, on the assumption that improved U.S.-North Korea relations would benefit inter-Korean ties. Both Tokyo and Seoul, however, are concerned that any U.S.-North Korea summit that sidesteps the question of denuclearization would set a dangerous precedent.

North Korea, meanwhile, is deepening its ties with Russia, cemented by its deployment of troops to Ukraine. On May 9, North Korean forces participated for the first time in Russia’s annual Victory Day parade commemorating the Soviet Union’s victory over Nazi Germany. Pyongyang appears confident it can weather its current difficulties by leaning on China and Russia, and sees no urgency in accepting Trump’s invitation to meet. It is also recasting its relationship with South Korea as an “adversarial relationship between two states” — a relationship without any goal of unification — and is amending its constitution accordingly. This will likely cement what amounts to a North Korean version of the Two Koreas policy.

The challenges facing Japan and South Korea are formidable. Many South Koreans are concerned about Japan’s constitutional revision and military buildup under Takaichi. Yet South Korea itself ranks fifth in the world in military capabilities, roughly on a par with Japan, and actively promotes arms exports and a strong military as national policy. The question worth asking is whether this is the moment for Japan and South Korea to seek a shared understanding that frames their combined military capabilities as a public good for the region?

All of this underscores the importance of Japan and South Korea building a more durable framework for communication, information-sharing and meetings between their governments. Progress on historical issues, which continue to cast a long shadow, remains necessary, not least because civil society ties are what ultimately underpin the relationship between states.