re: Afghanistan and nations
The UN okayed an invasion of Afghanistan because the 9/11 had an obvious connection with the Taliban regime. It wasn't too difficult to convince the Security Council about this; there were also training camps in tha t country and OBL was there, too.
So, Afghanistan under the taliban was a threat.
As for non interference in internal matters of a sovereign state, it has a lot to do with the notion of what a state or a nation is.
2 countries, with a common border, can have entirely different histories and each choose different ways of dealing with their population.
But I'll come back to it later.
Raoul