America's alliance with South Korea is in crisis. Strangely, few in Japan seem to have noticed, let alone grasp, what it portends for their country. Japan is now on the spot in a way that was not the case during the Cold War.
No alliance can survive unless it rests on a congruence of strategic interest and a willingness to share risk. The U.S.-South Korean alliance was a consequence of the Korean War, representing a huge shift in the global balance of power after Soviet leader Joseph Stalin had brought the Cold War to East Asia. But the East Asian balance is now shifting again, as a consequence of the end of the Cold War.
These new strategic circumstances have eroded the congruence of interest between the United States and South Korea. That's because the two parties no longer see the North Korean problem through the same lens.