Its OUR mess. We made it, ISIS is a American creation just like Al-Quaeda is. We removed the stability the region once had, even though it was a brutish stability [SADDAM] it was still stable. Saddam just was not working with us as far as our *ahem* "strategic interests" go [Oil], so his butt was removed as soon as the first excuse was available to do so. When we did that we also disbanded the relatively well-trained Iraqi Police force and Army, so the police force was now American...We leave and the shit hits the fan. Is anyone really fucking surprised here ???
If overnight, the Police force AND the Army AND the national guard/coast guard was instantly removed from every town and city in the US, shit would hit the fan pretty fast here to. Gangs would dominate, the KKK would probably make a resurgence as a stabilizing force in some areas, likewise for black panther groups and other ethnic or religious groups.
Thats what we created in Iraq with the exception of Shiite Areas [South East Iraq] - they are happy they have control of the government there and Shiites blindly follow their Shiite government...Beyond that, Iraq is a power vacuum in Sunni areas[Western Iraq]. It just so happens that Western Iraq also shares a border with Sunni majority Eastern Syra, which due to civil war East Syria also has a power vacuum...Bingo, ISIS is born. Another American creation has breathed the air of the Middle East, and once again we must "stop" this evil.
The proper thing to do imo, is to backup Assad. Let the guy rule his country, he is 100x better than any Jihadi is. That alone will contain ISIS to Western Iraq, and from there I guess let the Kurds police that region of Iraq. Stability will be much better from that alone.