The US is pushing the militaries of South Korea and Japan to cooperate in the face of aggression by North Korea and China's military buildup. The two are allies of the US. Why not each other?
Can Japan and South Korea ever be military partners, even allies?
Each nation is a democracy. They are already allies individually with the United States. Each trains with the American military separately in joint naval exercises.
Most of all they are close neighbors in the tough neighbor of Northeast Asia that includes North Korea, China, and Russia. The threat of North Korea someday launching a nuclear-tipped missile toward either country should have had the effect of drawing Japan and South Korea closer.
But as much as the United States wants the two countries to cozy up, history has long kept them apart.
Imperial Japan’s colonization of a then-unified Korea in the early 20th century remains a strong memory among Koreans. The two also claim two small islands in the sea between them (the “East Sea” to Korea, the “Sea of Japan” to Japan).
As a small country surrounded by big ones (or a “shrimp among whales,” as Koreans say), South Korea believes it is best to be remain close to the benign giant across the Pacific, America.