The Spread of Islam began shortly after the death of the Islamic prophet Muhammad in 632. Trade networks connected many regions which helped the spread of Islam. During his lifetime, the community of Muslims, the ummah, was established in the Arabian Peninsula by means of conversion to Islam. In the first centuries conversion to Islam followed the rapid growth of the Muslim world under the Rashidun and Umayyad Caliphs. Muslim dynasties were soon established and subsequent empires such as those of the Abbasids, 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. Today there are between 1.1 billion and 1.8 billion Muslims, making Islam the second-largest religion in the world.