The initial impetus of the Crusades is when the Muslims began robbing and molesting Christian pilgrims.
Actually, no it was not. It was when Islamic armies began conquering Christian communities, impressing women into sexual slavery, and forcing the conquered people to convert or die.
What we see ISIS doing right now is the same activity which ignited the crusades.
This is well documented in archeology and in both western andMuslim histories. Academia didn’t begin trying to push the Christian agressor revisionism until the nineteen seventies, and the scholarship backing the revision has been pretty much the same as the congruent attempt to paint the Aztec and Incan empires as pacifist utopias.