[Antoninus]

Egypt used to be part of the Greek Empire, and it's fall was one of the reasons the Crusades were launched.

Actually, Egypt fell in the 7th century. The first crusades weren't launched until the late 11th century. The main instigating factor was the burning of the Church of the Holy Sephulcre in Jerusalem and the increasing military weakness of the Byzantine state after the disastrous Battle of Manzikert in 1071.

[Pelayo]

I know when it fell, I ment in the general sense the destruction of the Empire was one of the events that precipated the Crusades. That it was not a single event as we would out it is un-important.