T. Greer at The Scholar's Stage has a characteristically long post about ISIS, taking off from the much-discussed Graeme Wood article in The Atlantic (that I haven't read). On a quick read, I agree with some of what T. Greer says, but I am leery of his endorsement of the analogy between the current struggles within Islam and the Reformation. (D. Nexon, I believe, is also opposed to the analogy, and he knows more about the Reformation than I do. I can't say I recall the *precise* grounds on which Nexon opposes the analogy, without refreshing my memory by looking at the relevant passages in his book or other writings, which I'm not going to do right now.)
Speaking for myself, I'm uncomfortable about an analogy between the religious struggles within Christianity (Christendom? whatever) of the 16th and 17th centuries and the struggles within Islam today. For one thing, the Protestant reformers were not trying to recapture an historical golden age by recreating a territorial entity under their control -- i.e., no analogy to the restoration of the Caliphate. That is just one difference. I'm sure there are others.
ETA: Such as differences in the content of the ideologies and the methods.