How far will the United States and South Korea go to assuage a petulant and threatening North Korea? The answer to that question has profound consequences for Japan — and the signs are troubling. Last weekend, the two governments said they would postpone joint air exercises as a gesture to Pyongyang, which demands that all such exercises — and anything it considers signs of a "hostile policy" — be ended if diplomacy is to continue. Diplomacy is important but Washington and Seoul must not give the North a veto over what is or is not needed for their mutual security.

North Korea has long insisted that the root of its problems with the world is "the hostile policy" of the U.S. This, Pyongyang claims, has forced it to cheat on its international obligations and develop a nuclear weapon and to defy the United Nations by testing and developing missile capabilities. That is a self-serving and hypocritical rationalization, one that ignores the threat that the North poses to its neighbors through its fiery rhetoric, physical attacks on their assets, cyberattacks, the abduction of innocent foreigners, extortion and other crimes.

U.S. President Donald Trump has tried to rhetorically disarm the North by meeting with the country's leader, Kim Jong Un, and offering to create a new bilateral relationship. The first step in that process was the June 2018 Singapore summit between the two men, in which Trump said he would cancel U.S.-South Korea military exercises to build trust. The North insists that the offer was open-ended and considers any attempt by Seoul and Washington to ensure that their alliance remains effective a betrayal of that offer.