The Islamic conquests of areas outside Arabia began in the seventh century. In the first wave of conquest, the Arabs took Syria, Egypt, and the Sasanid Empire. In the late seventh and early eighth centuries, Islamic forces took Tunisia, Spain, Algeria, Morocco, and Sind. Common explanations for the rapidity of the Muslim advance include lust for treasures and valuables, religious devotion, and the weakness of the foes of Islam. The most convincing explanation finds the causes of Muslim expansion in the talent of the Muslim leaders and the structure of Arab society. During the period of expansion the Arab forces were organized into regular, paid armies and kept in military camps and garrison towns so that they did not overrun the countryside. The Arab Muslims became minority rulers, thinly spread over non-Muslim societies that they dominated and taxed, but did not try to convert.…