There have been infighting among factions of Islam for a long ass time. This was before the Crusades obviously with an Imam I forget the name of, where Shiites and Sunnis probably originally separated IIRC because I can't be bothered to look it up or anything. When the Crusades happened, Islam didn't stop its divisive infighting lol. Neither did the underlying distaste among Europeans fighting under a Christian flag. That is something that should be obvious, as humanity is never completely unified (the US sure is not unified).
I knew here was a total slaughter at Acre, not much more from what I remember in Highschool, but I went to probably the most liberal highschool in the state lol. It certainly was the best as indicated by the rankings over the last 20 odd years of it being in existence as an academically gifted magnet school. They didn't cover the Crusades that much, but we learned it was a massive embarrassment and that there was infighting of course. That doesn't change the overall motivating factor of the whole thing, which was the whole Ishmael versus Jacob (Israel) as rightful owners of Isaac (and Abraham's) legacy and the land formerly known as Canaan. Wooohoo for tribal infighting that still occurs to this day. Muhammad built his temple on the site where the people think the Arc of the Covenant might be lol. That also used to be Solomon's temple (redone by Herod during Roman times). So much bullshit over there its not funny, and people who still buy into it seriously to boot. Might as well kill them all.