One, the Holocaust had NOTHING to do with Christians. That was pagan German Nazis killing Jews.
The Crusades were a defensive war against muslims that had conquered the Middle East. They took back the Holy Land.
Luke 22:36 - Then said he unto them, But now, he that hath a purse, let him take it, and likewise his scrip: and he that hath no sword, let him sell his garment, and buy one.
How hard is this to understand ? Self-defense is certainly allowed.
I am sayine Crusades were Political not from any biblical scripture