Japan and South Korea do not need to like each other to prepare for the same crisis.
That is the useful lesson from the unlikely Franco-Russian alliance of the 1890s. Republican France and czarist Russia had little ideological affinity, but both feared isolation in the face of a stronger Germany. Their partnership grew through military planning, logistics and clearly defined commitments — not sentimental declarations.
Tokyo and Seoul face a similar strategic problem. A conflict over Taiwan could draw Japan in through geography, U.S. bases and sea lanes. At the same time, North Korea could exploit the distraction with missile tests, cyberattacks or limited military action against the South.
A formal Japan-South Korea alliance is politically unrealistic. Colonial history, territorial disputes and domestic constraints make that clear. But the absence of an alliance does not justify the absence of planning.
The practical agenda is obvious: missile warnings, cyber defense, maritime surveillance, evacuation plans, fuel, medical transport, port access and repair capacity. A limited logistics agreement could produce more security than another summit statement.
The key is to build procedures before a crisis. If Taiwan is blockaded while tensions rise on the Korean Peninsula, officials will not have time to negotiate basic coordination from scratch.
Safeguards would be essential. Cooperation should not create automatic obligations to fight, allow Japanese forces into South Korea without consent or bypass parliamentary oversight.
The historical analogy also carries a warning: alliances can entangle states as well as deter enemies. The goal should therefore be resilience and crisis management, not an open-ended military pact.
Japan and South Korea remain divided by history. China, North Korea and Russia have every incentive to exploit that division. Limited, functional cooperation would not erase the past. It would prevent the past from becoming a strategic vulnerability.
