Ukrainian President Volodymyr Zelenskyy is asking South Korea for weapons and air defense systems as North Korea deepens its military support for Russia’s war in Ukraine. Seoul should listen carefully — but it still should not say yes. South Korea has every reason to be alarmed by the expanding military partnership between Pyongyang and Moscow. North Korean troops have been deployed to Russia, while North Korean ballistic missiles and other weapons are reportedly being used on the battlefield. In return, Pyongyang stands to gain things it has long sought: combat experience, military know-how and advanced Russian technology. The prospect that North Korean forces could return from Ukraine better trained in modern warfare is a direct security concern for Seoul. That does not mean South Korea should cross the line into supplying lethal weapons or sophisticated air defense systems to Ukraine. Seoul’s restraint is not indifference toward Ukraine. It is a sober calculation of its own survival. Zelenskyy’s appeal is understandable. Ukraine is fighting for its territory and sovereignty,