21.

 What effect did this development have on the Byzantine Empire?

            The Eastern possessions were lost to the Byzantine Empire, and the three ancient Patriarchates of Jerusalem, Antioch and Alexandria came under infidel control. Byzantium was under constant attack from Mohammedan forces, and although it withstood this onslaught for eight centuries more, it finally succumbed in 1453. Christianity survived, but with difficulty.