[After some other posters made casual remarks touching on the atrocities committed by Christian crusaders.]
Then you are grossly historically ignorant.
The crusades were a military response to a broad-sweeping Muslim invasion of Christendom that had been ongoing for over a century. Christian cities and settlements were waking up each day finding themselves surrounded by a sea of scimitar-waving conquerors. They completely obliterated the Eastern Christian Empire of Constantinople. letters were sent pleading for succor from their fellow Europeans. The Crusades were the response.