Although he reigned for only two years, Bakr helped unify the Arabs and made way for his successors, who set out to expand the empire in Iraq, Syria, and Egypt, where they easily wrested control from the pagan Sassanians of Persia, and later the Christian Byzantines. Modern scholars say the Arabs' rapid military success owed more to fortuitous politics than to religious fervor. "People were willing to accept the Muslims because they were fed up with the previous rulers," John Renard, author of In the Footsteps of Muhammad: Understanding the Islamic Experience, says of the competing Persian and Byzantine regimes.
Indeed, their armies had become exhausted fighting each other. Factional conflict in Persia had further worn down Sassanian power, while the Syrian and Egyptian subjects of Byzantine rule had become alienated by the religiously intolerant Greek Orthodox priesthood. In contrast, the conquering Muslims didn't require their Christian and Jewish subjects to convert, only that they pay a special tax for their right to practice their own religions.
Nor did the Muslims try to reinvent the political or administrative wheels of the lands they conquered. The Muslim caliphs imposed Arabic as the official language and minted their own coinage, but they allowed those of other faiths to serve as civil administrators within the Islamic state. The policy allowed life to continue largely as it had, and it reduced resentment of the conquerors.
Further, by allowing all members of society to compete for positions in government, "[the Muslims] set up a new social dynamic in which the criteria for selection was based on competence," says George Saliba, a professor of Arabic and Islamic science at Columbia University. "People were allowed to advance according to their talents. And the result was that they [enhanced] the empire's knowledge base."
It had all the ingredients for a sumptuous societal layer cake: a common language and currency to give it bureaucratic consistency and a flourishing polyglot of cultural and religious diversity to give it social spice.
Nowhere was that more the case than in Baghdad's fabled House of Wisdom, which in the late eighth century became the center of learning in the Muslim world. Overseen by the Abassid caliphate, it drew scholars and intellectuals from throughout the empire. Unfettered by ethnic caste or religious dogma, the best and the brightest were given the freedom to explore the frontiers of science and mathematics and plumb the depths of ancient Greek philosophy and literature.
What united this society most, however, was trade, not merely in books and texts, but in all the riches of a vast empire: textiles and steel blades from Persia, silk and gunpowder from China, spices and tea from India. "It would be wearisome to prolong the catalog," John Glubb writes in his book The Life and Times of Muhammad. "Suffice it to say that for five centuries after Muhammad, the Muslims dominated the world both culturally and militarily as completely as Europe and America have done for the last 250 years."
That is not to say, however, that Islam's so-called Golden Age was an unbroken chain of peace and prosperity. Infighting between rival caliphates sent the center of Muslim rule from Mecca to Damascus to Baghdad and then to Cairo, which even today remains the urban center of Muslim life and intellectualism. That is thanks, in part, to the al-Azhar mosque; founded in 970, it is considered by many to be the world's oldest university.
The dawning of the new millennium, however, marked the beginning of the end of the Muslim empire. Although the Christian Crusaders were vanquished in 1187, soon a new, even greater threat converged on the empire's eastern borders. Genghis Khan and his marauding Mongols quickly overran Baghdad, killing 10,000 people. Remarkably, the Mongols themselves eventually fell under Islam's spell, converting to the faith and eventually becoming some of its leading patrons.