Everyone should read Graeme Wood's piece in the new Atlantic: "What ISIS Really Wants".
Wood shows that ISIS is an unquestionably authentic — if utterly murderous — reading of Islam. He also, should there be doubt about it, makes it clear that ISIS does not speak for all of Islam.
As I read the piece, the first I know of to stress the importance of the caliphate to Islam and its centrality for ISIS, the following analogy occurred to me. Just as there are whole chunks of Islamic observance that remain latent without a caliphate, so too are there whole aspects of Talmudic Judaism that remain latent without a Temple, a high priest etc..
It's just an analogy, terribly imperfect. And, to be absolutely clear, there's nothing in Jewish life, even at its worst, comparable to ISIS. For one thing, Jews have lived in and helped shape the secular world for too long for Third Temple fanatics to gain the same kind of traction that ISIS has achieved among so many Sunni Muslims, Allah be screwed.
And there is nothing I know of in Talmudic Judaism so hot for slaughter as there is in the variant of Islam rearing its head in the form of ISIS. Were a Third Temple to arise in twenty-first century Jerusalem it would of course provoke mass killing between Israel and the entire Muslim world, probably involving global nuclear Armageddon. But putting that detail aside, there is nothing intrinsic to Third Temple Judaism a la the Talmud that ordains beheadings etc. a la ISIS. A Third Temple would be bad news for animals — the sheep, goats, chickens lining up to be sacrificed — but not necessarily, say, for Bedouins, at least no worse than they now endure.
The Graeme Wood piece demonstrates beyond doubt that ISIS can't be fully explained or explained away by reference to America's invasion of Iraq, disastrous as that was; tribal differences among Arabs dating back to the 6th century; national differences abetted or deriving from colonialism.
Wood shows that a key force behind ISIS is religious belief per se, fanatic belief, may Christ have mercy on our souls.