I would probably say that byzantine empire helped influence their growth. As it grew the muslims were targeting it. Euroupe during this time was not very well defended. So when the byzantine empire started falling the europeans started fearing their spread so they saw them as a threat. This is what made them grow in strength and start making bigger armies. As the armies got bigger so did muslims spread. They had taken over jerusalem calling it muslims only in that spot. So everyone in euroupe started struggling to rally against this threat. It was during this age these rallies were called crusades. They eventually came to a peace treaty to stop all attacks and let christians go in the city of jerusalem again. But they didnt relinquish control over it.
