By the beginning of the eleventh century the crescent of Islam had flown from the Iberian heartlands to northern India. How can this rapid and remarkable expansion be explained? The internal view of Muslim historians was that God supported the Islamic faith and aided its spread. The external, especially European, view was that the Muslim concept of jihad (JEE-hahd), or struggle, was the key element. The Qur’an does not precisely explain jihad. Some Muslim scholars hold that it signifies the individual struggle against sin and toward perfection on “the straight path” of Islam. Others claim that jihad has a social and communal implication — a militancy as part of a holy war against unbelievers living in territories outside the control of the Muslim community.

Today, few historians emphasize religious zeal alone but rather point to a combination of the Arabs’ military advantages and the political weaknesses of their opponents. The Byzantine and Sassanid Empires had just fought a grueling century-long war and had also been weakened by the plague, which hit urban, stationary populations harder than nomadic populations. Equally important are the military strength and tactics of the Arabs. For example, rather than scattering as landlords of peasant farmers over conquered lands, Arab soldiers remained together in garrison cities, where their Arab ethnicity, tribal organization, religion, and military success set them apart. All soldiers were registered in the diwān (dih-WAHN), an administrative organ adopted from the Persians or Byzantines. Soldiers received a monthly ration of food for themselves and their families and an annual cash stipend. In return, they had to be available for military service. Fixed salaries, regular pay, and the lure of battlefield booty attracted rugged tribesmen from Arabia.

The Arab commanders recognized the economic benefits of capturing the major cities of the region. Arab caravans frequented the market towns of southern Syria and the rich commercial centers of the north, such as Edessa, Aleppo, and Damascus. Syria’s economic prosperity probably attracted the Muslims, and perhaps Muhammad saw the land as a potential means of support for the poor who flooded into Medina. Syria also contained sites important to the faith: Jerusalem, where Jesus and other prophets mentioned in the Qur’an had lived and preached, and Hebron, the traditional burial place of Abraham, the father of monotheism.