I wish I could give you a better response, I agree with almost everything you have said so far. Religion itself lends to these kinds of ideas, you rarely see a "prophet" come about who isn't claiming armageddon. Or the idea of the rapture, where we good christians will ascend into heaven while all of you unbelievers will burn eternally in fires made especially for your sins.

When you make a finality like that, believers will kill. The crusades being an example or organised religious geo-political action. But it goes both ways, consider the Islamic invasion of europe foiled by mainly Polish armies ~1600bce. And Islam makes a special claim that no other religion ever did--it claims to be the last and final religion. Claims, anyway

Politically speaking, I believe the difference is that we don't let that shit run our governments anymore. Before the separation of church and state we had witch hunts and burning them alive, for heresy. Now, we have the fucking pope openly accepting gays. Times have changed, but islam is stuck in a brutal, bullet riddled situation. And I don't see it ever changing. These types of conversations were surely had by leaders during the Crusades.