Trump: US can't go on being the policeman of the world!

So, this is now the fact on the ground:

https://timesofindia.indiatimes.com/world/us/us-cant-be-worlds-policeman-trump-to-us-troops-in-iraq/articleshow/67268197.cms

But, the interesting question is this:

Whoever asked the US to be the policeman?

What entity authorized the US to be the policeman of the world?

The world would be so much happier if the US did not put its nose into the affairs of sovereign nations by direct interference as in Afghanistan by putting marines into the field or indirect interference as in Iran by sanctions.

And when will the US pull its nose out the Israeli/Palestinian dispute.