Caliphate

A caliphate is the Islamic form of government representing the political unity and leadership of the Muslim world. The head of state's position (Caliph) is based on the notion of a successor to the Islamic prophet Muhammad's political authority.

Caliphate in "Islands in the Sea"
Under the Umayyads, the Caliphate grew rapidly geographically. Islamic rule expanded westward across North Africa and into Hispania and eastward through Persia and ultimately to Sindh and Punjab. Its crowning achievement was the conquest of the Roman Empire and the fall of Constantinople.

Subsequently, the Caliphate was able to expand Islam into Europe at the expense of Christianity.