A fast-escalating trade war between South Korea and Japan took a dangerous turn this week when the Koreans abandoned a military intelligence-sharing agreement with the Japanese, weakening an important source of information on North Korea and China. South Korea said it was responding to Japan’s restrictions on trade with South Korea, including on the export of specialized chemicals needed to make components for electronic devices . Japan described the move as a tightening of controls over critical materials, but it went far beyond that.

The rupture has little to do with national security, important materials, mismanagement or any of the other proffered rationales. It’s all about age-old animosities, and they’ve been allowed to putrefy in large measure by President Trump’s irresponsible attitude toward trade and alliances.

This is a fight in which everyone stands to lose except China and North Korea, and the Trump administration should be heavily leaning on its closest Asian allies to come to their senses.

The roots of the animosity stretch to Japan’s colonization of Korea between 1910 and 1945, and more specifically the brutal exploitation of Koreans as sex slaves and forced laborers during World War II. Passions have flared regularly but have usually been tamped down through the alliance of the two democracies with the United States against threats posed by North Korea and China, and by the extensive trade between South Korea and Japan.