The people of the Islamic world created numerous sophisticated centers of culture and science with far-reaching mercantile networks, travelers, scientists, hunters, mathematicians, doctors and philosophers, all contributing to the Golden Age of Islam. Islamic expansion in South and East Asia fostered cosmopolitan and eclectic Muslim cultures in the Indian subcontinent, Malaysia, Indonesia and China. As of October 2009, there were 1.571 billion Muslims, making Islam the second-largest religion in the world. The expansion of the Arab Empire in the first centuries after the Islamic prophet Muhammads death soon established Muslim dynasties in North Africa, West Africa, to the Middle East, Somalia and in Iran. Early Caliphs and Umayyads: this was the time of the life of Islamic Prophet Muhammad and his early successors, the four Rashidun Caliphs. Within the first century of 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 one of the most significant empires in world history.
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. Islam was introduced in Somalia in the 7th century when the Muslim Arabs fled from the persecution of the Pagan Quraysh tribe. When the Muslims defeated the Pagans, some returned to Arabia, but many decided to stay there and established Muslim communities along the Somali coastline. The local Somalis adopted the Islamic faith well before the faith even took root in its place of origin.
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. The Abbasids: this was the time of the Abbasid Dynasty, the second great dynasty with the rulers carrying the title of Caliph. Expansion ceased and the central disciplines of Islamic philosophy, theology, law and mysticism became more widespread and the gradual conversions of the populations within the empire occurred. Significant conversions also occurred beyond the extents of the empire such as that of the Turkic tribes in Central Asia and peoples living in regions south of the Sahara in Africa through contact with Muslim traders active in the area and Sufi orders.
In Africa it spread along three routes, across the Sahara via trading towns such as Timbuktu, up the Nile Valley through the Sudan up to Uganda and across the Red Sea and down East Africa through settlements such as Mombasa and Zanzibar. These initial conversions were of a flexible nature and only later were the societies forcibly purged of their traditional influences. The result of this, he points out, can be seen in the diversity of Muslim societies today, with varying manifestations and practices of Islam.
Conversion to Islam also came about as a result of the breakdown of historically religiously organized societies: with the weakening of many churches, for example, and the favoring of Islam and the migration of substantial Muslim Turkish populations into the areas of Anatolia and the Balkans, the social and cultural relevance of Islam were enhanced and a large number of peoples were converted. This worked better in some areas and less in others Throughout this period, as well as in the following centuries, divisions occurred between Persians and Arabs, and Sunnis and Shiites, and unrest in provinces empowered local rulers at times. Islam was initially associated with the ethnic identity of the Arabs and required formal association with an Arab tribe and the adoption of the client status of mawali. and c. 930 a law was enacted that required all bureaucrats of the empire to be Muslims.