having a neighboring country with nuclear weapons and run by a madman is dangerous. Why didn't they think about that 10 y years ago?

Well, better late than never.

China would be FAR less threatened by a unification of Korea under democracy than the current North Korean lunatic regime.

I would propose a compromise:

The NK regime is removed.

All Korea re-unites under democracy.

Krazy Kim is given assylum somewhere with his henchmen, preferably in Cuba, Vietnam, Laos or some other Marxist shithole.

All USA & other foreign forces are withdrawn from Korea.

The new United Korea reduces its military to 300,000 (a 50 % reduction, not counting the worthless skeleton army of North Korea) or even 100,000.

This is a win for everybody EXCEPT Krazy Kim. He might agree to it, though, if the alternative were annhilation by China.