[PoBoy321]

My understanding, and of course I could be wrong, was always that after the rise of Mohammed in 711, Islam spread throughout the Middle Eastern world basically by Muslim warriors approacing a city, telling them that they had to pay taxes to them. If they accepted, they paid the taxes and basically everyone was ok. If they refused, they were attacked, conquered and forced to pay.

The Crusades were a military conflict with the sole purpose of destroying as many Muslims as possible and driving them out of Jerusalem.