Actually, MGD, I think you'll find the Umayyad caliphs kicked things off when they expanded their empire through then-Christian North Africa soon after Mohammad's death, crossed into the Iberian peninsula in 711 and fought their way up to Poitiers before being halted by Charles Martel. The Crusades were a response to that rapid expansion, by 1095 a second front of which posed a direct threat to the Christian heartland of antiquity (Byzantium, i.e. modern-day Turkey).
The Truth about the Crusades | Raymond Ibrahim
That is what gave birth to the Crusades. They were not the brainchild of an ambitious pope or rapacious knights but a response to more than four centuries of conquests in which Muslims had already captured two-thirds of the old Christian world. At some point, Christianity as a faith and a culture had to defend itself or be subsumed by Islam. The Crusades were that defense.
Unfortunately the modern western fashions for self-flagellation, virtue-signalling and "white man's guilt" cause too many of us to swallow revisionism of the sort that seeks to lay all blame for the woes of the Muslim world at our feet.