I shall try doing this from memory rather than looking anything up but the downside is that I can recall very little of the facts.
There is, possibly, a parallel between the current unrest in the Middle East and the most lethal war in the whole of the 19th century, one which killed more people than the Great War. It doesn't often get mentioned, but it was a religious war and it killed about 40 million people.
It was started, and fought, by a group of fundamentalist evangelical Christians who were attempting to convert the population of China to their extremist form of Christianity. I have it in mind that it happened in the 1880s but I might be wrong. I've even forgotten what it's generally called in the history books.
Forty million dead, and the whole war entirely forgotten by people at large. They were, admittedly, foreigners, but even so.
I can't add much detail, not without looking. But I do think it's very like ISIS except it was fundamentalist Christians running berserk instead of fundamentalist Muslims.
This war could never have had such lethal consequences had China not first been softened up by Western destabilization and I do remember the name of that part - that was the First and Second Opium Wars, fought solely for the benefit of capitalist enterprise and on the cynical pretense that it would allegedly be good for the Chinese in the long run, which it very much wasn't.