What "World"?
ISIS is not a threat to the US more than any other terrorist group out there. They have been bottled up where they are, and going places where other terrorist groups have presence. they will be dealt with as the occasion arises. ISIS is no longer a threat to become a Caliphate and all that other crap they are dreaming while they smoke their hashish down there.
ISIS is an issue with those who want to feed their war industry friends and take their cut. Putin decided to take 'em down because they could become an issue in Chechnya. Helping Assad si an issue he has as much a right to do as we do to oppose him. Tough shit.