In the year A.D. 610, while meditating in a mountain cave above the town of Mecca, a 40-year-old Arab merchant named Muhammad ibn Abdullah saw a strange vision: An angel, Gabriel himself, commanded him, "Recite!" Stunned by what he saw, Muhammad fell to his knees in confusion. But the angel implored him again. "Recite!" the voice demanded.
It was an odd request of an illiterate man whose life had until then been defined not by godly pursuits but by his far more earthly talents as a businessman and mediator of tribal disputes. "What shall I recite?" Muhammad replied. To which the angel said, according to the Koran: "Recite in the name of your Lord who created, created man from clots of blood! Recite! Your Lord is the most bountiful one, who taught by the pen, taught men what they did not know."
The jolting message Muhammad carried to his fellow Meccans: The collections of idols they and their ancestors had worshiped for generations were false. And, as has been shouted ever since from minarets around the globe: "There is no god but God, and Muhammad is his messenger."
At first, the Meccans mocked Muhammad, calling his revelation fakery or the ravings of a madman. But when he announced subsequent revelations that condemned the nonbelievers to hell, their disbelief flared into outrage. Muhammad's one true God was not only an affront to their spiritual beliefs and ancestral heritage; it also threatened Mecca's social and economic order. If Muhammad was right, the tribal way of life, with its hierarchies and rivalries, was irrelevant. One God meant one people. And Muhammad, not the Quraysh chieftains, was its leader.
Under this new faith, the foundation for society was not tribal affiliation but religious brotherhood. It was a radical idea that would unite the warring Arab tribes and create a military and political power base that the Muslims, as they came to be known, would expand far beyond their Arabian roots.
Thanks in part to Islam's message of social justice and tolerance for other religions of "the book" (Judaism and Christianity), combined with growing unrest under the then dominant Byzantine and Persian rulers, the new faith would quickly win converts from Spain to China. Indeed, within a mere two centuries, Muslims would create the largest empire the world had yet known.
While Islam's rapid spread made it the world's fastest-growing religion, the conversion hardly happened overnight. Indeed, in the three years after Muhammad's first revelation, he is said to have convinced but 30 followers, mostly those of his own clan. Meanwhile, they were persecuted by the dominant Quraysh leaders, who forbade them to marry or even trade with tribal members.
But fortuitously, Muhammad was soon called to Medina (then Yathrib) to help mediate a struggle among five competing tribes. The Muslim migration to Medina in 622 marked the seminal event in Islamic history. Called the hegira, it "marks the beginning of a new polity," Jonathan Bloom and Sheila Blair write in their book Islam: A Thousand Years of Faith and Power. "For the first time in Arabia members of a community were bound together not by traditional ties of clan and tribe but by their shared belief in one true God."
Over the next decade, Muhammad worked to convert Medina's pagan, Jewish, and Christian tribes to his new religion. And a succession of raids on passing caravans won him more followers. Eight years after his flight from Mecca, he returned to his hometown with an army 10,000 strong. The Meccans surrendered without a fight, and Muhammad's triumphant army claimed the city for Islam.
But contrary to Arabian tribal customs that usually resulted in the beheading of losers and the enslavement of their families, Muhammad showed remarkable mercy to his Meccan opponents, demanding only that pagan idols be smashed. He didn't force the Meccans to convert to his new religion, but his pardoning of his opponents helped win them over voluntarily.
The resulting consolidation of Muhammad's power was short lived, however, because he died just two years after taking control of Mecca. He had no male heirs and had named no religious successor, or caliph, a void that sparked a power struggle that has dogged the faith ever since. Some considered Muhammad's son-in-law, Ali, to be his rightful heir—they would become Islam's Shiite faction—but another close friend, father-in-law Abu Bakr, was named the first caliph by Muhammad's closest disciples, beginning a long line of Sunni caliphs.