The Spread of Islam started shortly after the death of the Islamic prophet Muhammad in 632 AD. During his lifetime, the community of Muhammad, the ummah, was established in the Arabian Peninsula by means of conversion to Islam and conquering of territory. In the first centuries conversion to Islam followed the rapid growth of the Islamic world under the Rashidun and Umayyad Caliphs.
Muslim dynasties were soon established and subsequent empires such as those of the Abbasids, Fatimids, Almoravids, Seljuk Turks, Mughals in India and Safavids in Persia and Ottomans were among the largest and most powerful in the world. The Islamic world was composed of numerous sophisticated centers of culture and science with far-reaching mercantile networks, travelers, scientists, astronomers, mathematicians, doctors and philosophers, all of whom contributed to the Golden Age of Islam.
The activities of this quasi-political early ummah resulted in the spread of Islam as far from Mecca as China and Indonesia, the latter containing the world's largest Muslim population. As of October 2009, there were 1.571 billion Muslims, making Islam the second-largest religion in the world.
Increasing conversion to Islam paralleled the rapid military expansion of the Arab Empire in the first centuries after the Islamic prophet Muhammad's death. Muslim dynasties were soon established in North Africa, West Africa, throughout the Middle East and in Iran.
In the first last century the establishment of Islam upon the Arabian peninsula and the subsequent rapid expansion of the Arab Empire during the Muslim conquests, resulted in the formation of an empire surpassed by none before. For the subjects of this new empire, formerly subjects of the greatly reduced Byzantine, and obliterated Sassanid, Empires, not much changed in practice. The objective of the conquests was more than anything of a practical nature, as fertile land and water were scarce in the Arabian peninsula. A real Islamization therefore only came about in the subsequent centuries.
Ira Lapidus distinguishes between two separate strands of converts of the time: one is animists and polytheists of tribal societies of the Arabian peninsula and the Fertile crescent; the other one is the monotheistic populations of the Middle Eastern agrarian and urbanized societies.
For the polytheistic and pagan societies, apart from the religious and spiritual reasons each individual may have had, conversion to Islam "represented the response of a tribal, pastoral population to the need for a larger framework for political and economic integration, a more stable state, and a more imaginative and encompassing moral vision to cope with the problems of a tumultuous society."
Source: Wikipedia English, 20 February 2011