"Where does the movie show the Muslims invading and conquering Christian and Jewish lands, prompting the Christians to fight back?"
There was much omitted, Where was the part where the Crusaders captured a town and ate the children? Both sides did bad things but they thought they were doing good because it was for God and Kings.
"Where was the part where the Crusaders captured a town and ate the children? "
WHERE on EARTH did you get THAT story????