Foreign policy

North Korea launched an orbital rocket today.
Syria's Assad continues to kill Syrians.

I can't help thinking that America's foreign policy would be a whole lot simpler if we hadn't decided that we, without sanction from anyone, "bear America’s global responsibilities". (These are the words of John Bolton & John Yoo: Hands Off the Heavens... two of my least respected sources.)
WHAT "global responsibilities"???

Who, exactly, appointed us the world's policeman???
Why, exactly, do we insist on this role???

These questions fall under the rubric Things I don't understand.