In the National Interest, I think a bit about how conflict between North Korea and the United States might escalate to include regional players:
War on the Korean Peninsula is almost too horrible to contemplate.
Nuclear-armed adversaries, fighting in densely populated urban terrain, could cause humanitarian disaster on a scale that the world has never seen. But the scenario might grow even worse. The last time that the United States fought North Korea, the People’s Republic of China intervened with destructive effect. The war lasted for three years, with heavy casualties on both sides. While both China and the United States have worked hard to prevent a recurrence of this catastrophe, the two great powers remain at odds over the fate of North Korea, a disagreement that might yet lead to war.