The spread of Islam into the Maghreb is an example of Arab invasion of North Africa. The Arabs send Muslim army to Maghreb (modern morocco) to battle against Byzantines and allies, and finally conquer most of the North Africa were many Berbers (locals of Maghreb) join the Muslim army. After Arabs gain more power in the region, the Berbers are now ready to adopt and convert to Islam as well as the Arabic culture.
During the high Middle Ages, the Roman Catholic Church became organized into an elaborate hierarchy with the pope as the head in western Europe. He established supreme power.
The principle that government can only do what its people give it the authority to do is called "popular sovereignty," since the people, usually through representatives, are in control of the direction of the state.
