Interesting telescoping of a fascinating period.
It leaves out a good amount of the colorful means Islam had of expanding.
And the impression that the crusades provoked an awakening of the brutal Muslim means of expansion is humorous.
The Crusades were a response to muslim brutalities: typically defenseless towns were razed, totally destroyed. Women and children taken for the slave markets, and men and other "useless" persons killed on the spot.
Grab any of the dozen books available to fill in these gaps.
Fascinating reading.