> why can't China and the US join forces and militarily overrun DPRK? All sibling comments talking about things like buffer states are missing the forest for t

> why can't China and the US join forces and militarily overrun DPRK? All sibling comments talking about things like buffer states are missing the forest for the trees. You don't invade North Korea mostly because they have nuclear weapons. No sane US administration (sighs) is going to risk over a million dead civilians in Seoul, Osaka or Tokyo and the resulting global recession. For China, despite all the missiles NK lobs toward Japan, the reality is that Beijing is closer to Pyongyang than Osaka and likely has worse missile defense. A Japan with nuclear ambitions isn't high on China's priority list either. You can hand wave their shaky missile tech away as a threat to Japan and China but that's a lot of lives to gamble on and there's a real possibility they've smuggled weapons abroad as well (more likely chemical than nuclear but still bad).