Islam
The First Four Centuries
Islam was an uncomplicated religion, easily adopted and readily understood. This helps explain the rapid expansion of the religion. Also important was the zealous fervor of the early converts, and the relative weakness of their neighbors. Even so, the expansion of Islam in its first decades remains one of the most remarkable military and political and cultural accomplishments of any people in any era.
The Muslims conquered Mecca in 630.By 635 they were in Damascus. The following year, at Yarmuk, the Muslims routed a Byzantine army and most of Syria was opened to them. In 637 they defeated a Persian army and had conquered the entire Persian Empire by 650. Expansion continued eastward in the following decades, until the Muslims had spread through Afghanistan and India, up to the borders of China.
Jerusalem fell in 638, Egypt in 641 (Alexandria held out until 642). The Muslims swept across North Africa, conquering Tripoli in 647, Carthage in 698, and entering Spain in 711. They were at the gates of Constantinople in 673 and again in 717, but the Byzantines managed to drive the Muslims out of Asia Minor again, and that area remained Greek until the 11th century.
These conquests were achieved under the Umayyad caliphs. Caliph means "vicar" or "successor", the title taken by Abu Bakr who succeeded after Muhammad died. He was followed in 634 by Omar and then Uthman, after whom the dynasty is named. The Umayyads ruled a single, unified Islam until the middle of the 8th century.
In 750, rebellion broke out. The descendants of Abbas, an uncle of Muhammad, managed to kill the caliph and most of his family. The Abbasids set themselves up at Baghdad, but rivals arose elsewhere and Islam fragmented politically. The one surviving member of the Umayyads fled to Spain where he continued to claim to be caliph at Cordoba (755). Another caliphate arose in Morocco in 788, one in Tunisia in 800, in Persia in 820, and in Egypt in 868. Each was ruled by a man who called himself caliph--successor.