I was thinking that this ISIS mess reminded me of the Khmer Rouge mess many years ago. The U.S. pulls out of an area, and murderous hell hounds move in.
In the case of the Khmer Rouge, we stayed out, and let the murder happen. Later, we wrung our hands about how it could have happened, amid much finger pointing. (Please excuse the mixed metaphor of hands being wrung and fingers being pointed. You can't quite do both at once, but I guess you can alternate.)
One of the problems is that once we touch it, we feel that everything that happens there is our responsibility. But, we do seem to go in making promises. Take our side, people, and everything will be better. And it works for a while, to some extent. Then, sometimes, we get tired of being there. And we pull out. And some of the people who took our side take a terrible beating.
It's tough being the world cop,
and hard to know when to stop.