Flashpoints | Diplomacy | East Asia

EU-Japan-South Korea Cooperation Is Indispensable Now

The trilateral is more feasible – and more important – than ever before.

For decades, South Korean strategy rested on a stable hierarchy within the international order. The alliance with the United States provided security; Seoul then managed relations with Japan, Europe, China, and regional institutions around that anchor. The alliance remains indispensable, but Seoul can no longer assume that this foundation will stay stable.

The evidence is visible in the way Washington now deals with allies. In 2025, the United States initially announced sharply differentiated “reciprocal” tariffs on South Korea, Japan, and the European Union. Negotiations later produced a 15 percent baseline framework for all three, but the process mattered as much as the final rate. Trade access, industrial investment, defense procurement, and alliance politics were increasingly handled as one bargaining package. Allies were not exempt from economic pressure because they were allies.

At the same time, Europe and Asia have been building connections that would have seemed highly ambitious a decade ago. The European Union signed security and defense partnerships with Japan and South Korea in November 2024. This year, the EU and Japan launched a defense-industry dialogue, while the EU and South Korea signed a digital trade agreement and began implementing cooperation on maritime security, cyber and hybrid threats, information manipulation, space, and the defense industry. The strategic map is becoming more networked. 

The network, however, remains uneven. Japan already has a mature economic partnership with the EU and rapidly expanding defense-industry ties. EU-South Korea relations are deepening, but they still lack the density and regular strategic consultation found in EU-Japan ties. A trilateral format would therefore do more than add another meeting: it would reduce asymmetry among three partners whose capabilities are increasingly complementary.

South Korea, Japan, and the EU now face four converging challenges and pressures.

The first is demographic. South Korea is aging faster than any other OECD society; Japan’s working-age population has been shrinking for decades; and the EU’s fertility rate reached a new low in 2024. Demography is not a social-policy sidebar. It affects defense recruitment, industrial capacity, fiscal room, technological adoption, and the ability to sustain long-term commitments. Each actor is experimenting with immigration, automation, workforce policy, and welfare reform, but the security implications remain largely compartmentalized.

The second is concentrated economic dependence. None of the three can or should decouple from China. Yet South Korea’s experience after the THAAD deployment, Europe’s debates over economic coercion, and China’s export controls on gallium, germanium, and other strategic inputs have shown that interdependence can be converted into leverage. De-risking therefore requires more than national stockpiles. It requires shared risk maps, compatible certification, co-investment in alternative suppliers, and advance consultation before export controls or industrial subsidies create collateral damage among partners.

The third challenge is U.S. volatility. The United States is still the only actor capable of providing extended nuclear deterrence to South Korea and Japan, and NATO remains central to European defense. But dependence on U.S. power now coexists with uncertainty about U.S. policy. The classic alliance dilemmas of abandonment and entrapment are no longer opposite ends of a spectrum. Today, U.S. allies fear both being left out and being drawn into bargains or contingencies they did not........

© The Diplomat