1 - Should the US send troops to foreign countries to stop genocides? 2 - If so, should the US get UN approval?
I'll answer #2, since it's the simplest. NO. We are an independent, soveriegn nation. We do not have to get the UN's permission for anything. The UN is corrupt and full of countries that don't recognize human rights, so why should we get their approval for anything.
#1 - No. People in other countries need to learn the lesson we did when this country was still a bunch of colonies. You are responsible for your own protection ... even from your own government.
U.S shouldn't send military troops to foreign countries to stop genocide without the UN's approval. No military action can also take place without congressional approval. Genocide is still committed in the world because the world's leaders do not have the political will to stop it.