Sure it has. Most notably during the Cuban missile crisis. And the UN sends peacekeepers, doctors and provisions to trouble spots around the world.
Yet massive human populations are still dying due to starvation and disease.
And you are telling us the UN is what stopped the Cuban Missle crisis? Seriously?
The UN is active in peacekeeping roles around the world. Don't you know that?
List of United Nations peacekeeping missions - Wikipedia, the free encyclopedia
I am not necessarily for the UN - I have no real opinion - but to say they do nothing like some on this thread are saying is staggering ignorance.
The concept was good, the execution is what sucks.