The fundamental principle is NOT to interefere with internal matters of sovereign states.
No matter what happens inside a country, as long as it doesn't influence outside its borders, it's none of our business.

However, if there is indeed a request from the country, a threat outside of it, an obvious genocide, then the UN can interfere.
But it can't be outside its competence and what its members allow it to do.
Givent the world is made of very different regimes with very different agendas and desires, it's not an easy task.
And of course, the UN is the ideal scapegoat, isn't it?

"It is a little misleading to speak of the role of the UN. The UN is nearly powerless as an abstract entity or even as a representative of the world's nations. It can act, instead, only insofar as it is given authorization by the great powers, which means primarily the United States.

Raoul