been accepted as the original Urheimat of the Semitic languages by a majority of scholars. Rise of Islam The seventh century saw the rise of Islam as the peninsula's dominant religion. The Islamic prophet Muhammad was born in Mecca in about 570 and first began preaching in the city in 610, but migrated to Medina in 622. From there he and his companions united the tribes of Arabia under the banner of Islam and created a single Arab Muslim religious polity in the Arabian peninsula. Muhammad established a new unified polity in the Arabian peninsula which under the subsequent Rashidun and Umayyad Caliphates saw a century of rapid expansion of Arab power well beyond the Arabian peninsula in the form of a vast Muslim Arab Empire with an area of influence that stretched from the northwest Indian subcontinent, across Central Asia, the Middle East, North Africa, southern Italy, and the Iberian Peninsula, to the Pyrenees. With Muhammad's death in 632, disagreement broke out over who would succeed him as leader of the Muslim community. Umar ibn al-Khattab, a prominent companion of Muhammad, nominated Abu Bakr, who was Muhammad's intimate friend and collaborator. Others added their support and Abu Bakr was made the first caliph. This choice was disputed by some of Muhammad's companions, who held that Ali ibn Abi Talib, his cousin and son-in-law, had been designated his successor. Abu Bakr's immediate task was to avenge a recent defeat by Byzantine (or Eastern Roman Empire) forces, although he first had to put down a rebellion by Arab tribes in an episode known as the Ridda wars, or "Wars of Apostasy". Following Muhammad's death in 632, Abu Bakr became leader of the Muslims as the first Caliph. After putting down a rebellion by the Arab tribes (known as the Ridda wars, or "Wars of Apostasy"), Abu Bakr attacked the Byzantine Empire. On his death in 634, he was succeeded by Umar as caliph, followed by Uthman ibn al-Affan and Ali ibn Abi Talib. The period of these first four caliphs is known as al-khulafā' ar-rāshidūn: the Rashidun or "rightly guided" Caliphate. Under the Rashidun Caliphs, and, from 661, their Umayyad successors, the Arabs rapidly expanded the territory under Muslim control outside of Arabia. In a matter of decades Muslim armies decisively defeated the Byzantine army and destroyed the Persian Empire, conquering huge swathes of territory from the Iberian peninsula to India.