i'm pretty sure at least one of those crusades resulted in christian armies sieging/looting/pillaging/committing atrocities in christian majority cities on their long march to Jerusalem, with most of them starving or dying of dyssentery or deserting along the way. Most effective form of self defense I've ever seen. And even when they made it to Jerusalem, surprise surprise, turns out there was a lot of christians and jews coexisting with muslims and they all got treated as muslims by the invading armies.