i just want to add that america's absent strategy is actually it's strategy: america does not want anybody to win, and does not want peace in the region, but is playing everybody off against each other in order to create instability and fuel further conflict.
the status quo is america's endpoint.
so, don't be surprised if they end up harder to get out of the region than makes any sense, although i'll agree that they've burned so many bridges that they're running out of rivers to cross.
pick your cliche.
the policeman is not there to create disorder. the policeman is there to preserve disorder.
but, i also like to point out that iran is on to something in calling america the great satan. for, this is what satan does, in the mythological literature: he divides and conquers.
and, that's why people find it so hard to get their head around it. america is supposed to be the good guy, supposed to have an end point.
http://www.atimes.com/article/afrin-marks-point-collapse-american-influence-syria/