system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why the united nations doesn't authorize the removal of governments like North Korea's?
gpt
A lot of reasons. 

To start with, the UN isn't so much a world government as it is a collection of the world's governments, and they generally — generally being the key word here — frown on military action over a government's politics.

Second, the UN Security Council would have to approve military action for this to happen, and China (A permanent member with veto power) would never permit an invasion within its own sphere of influence. It's a lot easier to invade, say, Iraq when you have one Security Council member (The US) really pushing for it when the other members don't have a clear conflict of interest — which they most often always do.

Third, North Korea is a known nuclear power with one of the most massive artillery batteries just 30 miles from Seoul. They've been preparing for a military invasion since the "end" of the Korean War (Technically, it's still going on) and any victory from a military intervention would be pyrrhic at best.

TL;DR Politics and nukes.