The crusades helped drive some of the seljuk Turks out of the area, but (according to Wikapedia) "It also opened up byzantium to Latin aggression which was not always dedicated to Byzantium's enemies"
Also, the Fourth crusade (made up of Latin crusaders) sacked Byzantium and greatly reduced power in the empire.
He proclaimed it would be in November.
I believe Japans Bombing of pearl harbor had the biggest impact
