>I'm not saying it wasn't a factor, but various movements to 'purify' Islam predate the crusades.


Well, the day after Muhammad's death there was disagreements about what was pure and what was not.

I saw this comment in the same wikipedia article I mentioned:

"The appeal of Wahhabism to Muslims has been described as stemming from Arab nationalism, ..."


One thing I keep in mind is that no religious idea has ever taken off because it was a good idea in any factual sense.

It always takes off because a clear pragmatic application succeeds in some social/political situation and carries it.