South Korea’s other options are mediocre. Missile defense does not work well enough to absorb all the incoming missiles we anticipate from the North. And while it is important to continue talks with North Korea, there is little evidence that Pyongyang will accept a serious arms reduction treaty. American extended deterrence has worked for decades, especially as concerns China’s nuclear arsenal. But North Korea’s threat to nuke the U.S. homeland in a conflict casts doubt on the American guarantee. To participate in a Korean conflict, an American president would have to be willing to risk a nuclear attack on U.S. cities. It is hard to imagine the psychological and strategic pressures on a leader faced with such a decision.

Given all this, I think South Korean direct nuclear deterrence against North Korea is a growing possibility. In other words, South Korea will likely develop its own nuclear weapons. The U.S. opposes this, and South Korean nuclearization would probably end the Non-Proliferation Treaty regime for good. But South Korea is in a tight spot now, especially with Kim openly talking about pre-emption. Direct nuclear deterrence, for all the anxiety it would create, would be a better solution than airstrikes, which would likely ignite a war.