Fear of war has become a new constant for the Korean peninsula. On Monday South Korea initiated a military exercise in the Yellow Sea and North Korea threatened to retaliate. Seoul went ahead without any response from the North, but the region retains the feel of a bomb with an unstable fuse.
In the short term Washington has no choice but to uphold its alliance obligations to the South. However, Pyongyang’s increasingly erratic behavior offers a dramatic reminder of the most important cost of the unilateral security guarantee: the threat of war.