I have been wondering about the kinds of appeal inducing people joining up with ISIS and outfits like them. This blogger suggests some themes that might attract such people, and to possible reasons for US ambivalent relations to ISIS. Much food for thought.
After further thinking about that I believe that Peter is right. ISIS, the group now claiming a Caliphate, might have had roots in some sectarian scheme the CIA and the U.S. Special Forces were running in Iraq. But it has by now far exceed that realm. The Caliphate is based on original Wahhabi ideas which were in their essence also anti-colonial and at first directed against the Ottoman rulers.