Policing the world is exactly what the United Nations was created for. It is the body that should do this job- not any one country. The US just hasn't been willing to let it do that.
Recall that the original Gulf war was a UN-sanctioned operation- and Saddam was still under UN sanctions controlling his border and air space. There were UN inspectors on the ground in Iraq checking to see if he had WMD as Bush's claimed- so what happen? When they report there was none Bush orders them out and begins bombing Baghdad. And then we wonder why other countries don't like us.