How have America's demographics changed over the past century and what accounts for this
change?

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).

i believe it would be capitalism

your answer would be a) no nation can be economically self-sufficient.

stay in school!