Actualy, it was Latin Christendom. And they were supposed to help the East Romans/Byzantines but eventually sacked Constantinople. And I'm not even going to get into the targetting of the Jews in the Rhineland.
The Crusades were necessary. I just wish they had been carried out better.
PS. Soem opf my ancestors were fighting the Caliphate in the Caucuses intermittently from 650 to 737 ina series of wars that makes Tours look like the turning back of a Recon in Force.
"eventually sacked Constantinople"
Led by the Venetians who sacked the place and literally made off with some of the actual buildings of Constantinople.