Dome of the Rock, Jerusalem
Dr. Ondřej Havelka (cestovatel), CC BY-SA 4.0 , via Wikimedia Commons

Archaeological evidence and historical records from seventh century Arabia are sparse, and contemporary non-Islamic sources do little more than confirm the bare bones of Muhammad's historicity. According to the traditional foundation story of Islam, however, a man named Muhammad was chosen by Allah (God) to be his prophet. The angel Gabriel dictated the Qu'ran to him, which Muslims (followers of Islam) consider the eternal expression of God's will to mankind. The Qu'ran teaches radical monotheism and the Five Pillars: faith (shahada), prayer (salat), almsgiving (zakat), fasting (sawm), and pilgrimage (hajj).

Muhammad attempted to preach the message of the Qu'ran in the Arabian city of Mecca, but was forced out of the city by the local pagans. He went instead to Medina, a journey known as the "Hijra," where his message was more successful. Raising an army, he returned to Mecca, which then proved more receptive.

After Muhammad's death in 632, his followers were led by rulers called caliphs, the first four being Abu Bakr, Umar, Uthman, and Ali. Under their leadership, the Caliphate attacked the weakened Persian and Roman Empires, completely destroying the Persians and conquering approximately two-thirds of Roman territory. Damascus, the capital of Roman Syria, fell in 635. Two years later, Muslim forces defeated the Persians and captured their capital, Ctesiphon. That same year, Jerusalem surrendered. Alexandria, the second-largest Roman city, was conquered in 641. Tripoli, a port city in north Africa, was taken in 647, and the ancient Persian capital of Persepolis was captured in 650, permanently ending the Persian Empire. Carthage was taken in 698, granting the Caliphate full control of north Africa. Armies crossed the Straits of Gibraltar and captured Toledo in 712. The Caliphate soon stretched from Spain to the Indus River.

After these astonishingly successful military campaigns, a split emerged among Muslims about who was the rightful successor of Muhammad. Although most viewed all four caliphs as "Rashidun" (rightly guided), others believed Ali, who was Muhammad's son-in-law and of the same family tribe, was the only legitimate ruler. This led to a deeper theological schism within Islam, with the Sunni believing the caliph should be chosen by the "Ummah," the full community of Muslims, and the Shia believing the "Imamate" should be passed down only through Muhammad's family line.

A civil war took place, with Ali defeated by the governor of Syria, Muawiyah, who belonged to the same tribe as the third caliph, Uthman. Muawiyah founded the Umayyad Caliphate and the Sunni became ascendant in the Islamic world, although the divide between Sunni and Shia continues to this day.

The Umayyads were conquered in 750 AD by the Abbasid Caliphate, which made their capital in Baghdad, built near the ruins of the Persian capital, Ctesiphon. For about two hundred years, there was also a major Shia caliphate in north Africa called the Fatimid Caliphate, but it was conquered by the Ayyubids (a Kurdish dynasty nominally under the Abbasids) in the twelfth century. The Abbasid Caliphate retained nominal control of the Sunni world until the thirteenth century, when it was conquered by the Mongols.