Tokyo has justified the move on national security grounds, arguing, without providing much evidence, that some of the materials have been making their way to chemical weapons factories in North Korea and elsewhere. Framing the move in national security terms may help Tokyo avoid a World Trade Organization challenge and diminish international opposition more broadly. But Japanese Prime Minister Shinzo Abe admitted that the primary motivation is a series of recent South Korean court decisions requiring Japanese firms to compensate workers conscripted during Imperial Japan’s 35-year occupation of the Korean Peninsula. Already, assets belonging to two Japanese firms have been seized and are expected to be sold in the coming months. Seoul has rejected Japan’s request to settle the matter with third-country arbitration.
Japan, it seems, just can’t convince South Korea to let 80-year-old bygones be bygones. The U.S.-led regional alliance structure, along with the well-oiled regional economic system, may pay the price.
Added fun: the Russians are offering to step into the gap. Kids these days may consider South Korea to be the land of Samsung, Hyundai and Gangnam Style but it's had a fairly authoritarian past.
Americans have long enjoyed the benefits of hegemony through hard and soft power. With the decline of empire, hegemony slips... and when you don't have a healthy bureaucracy to advance American interests (for better or worse) you end up with a world less interested in America.