How did warfare and the constant threat of invasion in europe lead to the creation of feudalism?

the two colonies had the earliest laws mandating religious tolerance.

the conditions that made the byzantine empire vulnerable to attacks by the muslin turks were the sack of constantinople by western crusaders, the conquests of the sultanate of rum, presence of rival kingdoms and finally the set up of fiefdoms at the empire which were owned by the ghazis (turkish warriors).