> One thing I have never understood: why can't China and the US join forces and militarily overrun DPRK? I cannot think of a regime changing American military

> One thing I have never understood: why can't China and the US join forces and militarily overrun DPRK? I cannot think of a regime changing American military excursion in the last 60 years that resulted in the scenario that America wanted, with the possible exception of Grenada. That's a good reason to not invade.