The Islamic religion expanded throughout much of Asia, North Africa and into Europe fairly rapidly. Starting in the Arabian Peninsula, expansion really started after the death of Muhammad in 632. Not only did the new Islamic community, or umma, continue, but within the next 200 years, Islam spread throughout much of the region. Continued expansion led to significant Muslim influence and presence in Indonesia, China, India, Persia (modern-day Iran), Turkey, North Africa and Moorish Spain.
People of the Book
One reason that Islam was able to spread so quickly throughout the Middle Eastern region is that Islam was, in a sense, familiar. People of the region often were adherents of either Christianity or Judaism. Although there are significant differences in the religions, Islam, Judaism and Christianity are all considered religions based on the precepts of the Old Testament, or religions of the Book. This similarity made conversion attractive and easy, thus contributing to the early spread of Islam.
Neighboring Political Unrest
Islam was also able to take advantage of the political unrest in the neighboring regions of Byzantium and the Persian Empire. The two empires fought a series of wars ending in 627 with the Battle of Nineveh. The wars left the empires short of resources, and the people were exhausted. The Muslims, under the first Caliph, Abu Bakr, were able to conquer the area of the Persian Empire that corresponds to modern Iraq. Following his success, Abu Bakr turned his attention to the Byzantine Empire and conquered the region of present day Syria. Greatly expanded, the Muslims next turned to North Africa, where Egyptians were discontented with the Byzantine government largely over the question of conversion to Christianity.
Despite Islam's vast territorial gains through conquest, Islam could not have held the area without a massive army unless it had the consent of the governed. Islam accomplished this in several ways. Taxes were levied and effectively collected on non-Muslims providing a powerful incentive for conversion. However, the early Caliphs also understood the importance of integration and offered remission of taxes for those who performed service for the burgeoning Islamic empire. Moreover, the early Caliphs were adept at incorporating local customs and mores into their governance techniques, which allowed the local populace to feel less like a conquered people.
In the era of the earliest Islamic expansion, tribes were the basic model of community in the region. The early Islamic caliphs took a two-pronged approach to dealing with tribalism and thereby strengthened their position. In order to transfer loyalty from the tribe to the Islamic empire, individual members were rewarded with land for loyalty to the empire. Additionally, military units were comprised of members of different tribes. However, the caliphs also realized that tribalism could be useful. By ensuring the loyalty of key members of the tribe, the burgeoning Islamic empire gained the allegiance of the kinship group and used the notable tribe members for leverage over the group. Ultimately, it was due to good governance and savvy judgement that Islam was able to expand so far so quickly.