Religious and Political Conquest : As with most any civilization, Islamic civilization was significantly spread through military power. Strong armies, as well as a strong Muslim belief in spreading the faith, led to the conquering of many surrounding areas and lands.
Peaceful Conversion : While religious fervor was sometimes expressed through militaristic action, it could also be used for peaceful conversion. This brought many people (and their lands) into the empire.
Strong Governance : Islamic civilization was also known for having strong governments. These governments kept the empire stable