I think we have to understand , all of us here, that the root of the cause is ideological warfare. Most of DAESH volunteers have been influenced by salafist jihad ideology , as well as many are graduates of Wahabist schools of thought that have been propagated in Eurasia, Central Asia, the Middle East and even in the West. Syria is a battle ground for Saudi and Irani interests vis-a-vis by proxy. So long as both Saudi and Irani interests will conflict, they will use proxy engagements. For one is the Saudi offensive in Yemen, by the way , which we don't even hear in news media here in the United States.
It is not that black and white, actually. There are various interests and powers involved; the United States is undoubtedly placed in a precarious situation since she is involve in alliance with Saudi Arabia and at the same time courting Iranian favor with the recent nuclear pact agreement. An exercise in balancing interests with interests, i suppose, and power brokerage processes. An American habituation.