Due to mild fear of a strip search at the airport, I decided not to fly with Daniel Brown's A New Introduction to Islam. But it was worth the wait. In another fascinating section, Brown explains how the early holy warriors made ends meet:
[Caliph] 'Umar's predecessor, Abu Bakr, allegedly experimented with the distribution of expropriated land. The continuation of such a policy would have been disastrous to both tax and military policy, however, by removing land from the tax rolls and distracting soldiers from their martial duties. Consequently under 'Umar, subject populations retained title to their land, while expropriated lands became the common property of the conquerors. Proceeds from the land were then systematically distributed among the Arabs on the basis of how long they had been adherents of Islam... A participants in the early conquests might, for example, receive 3,000 dirhams per month, while an Arab who had joined the Islamic venture at a later time received a tenth as much.
Brown also observes that the conquerors discouraged conversion:
A seventh-century Iraqi Jew or Egyptian Christian curious to learn more about his new rulers might initially have found the task rather frustrating... 'Umar discouraged assimilation in several ways. In Iraq and Egypt he confined the Arabs to garrison cities... These cities were placed in such a way as to dominate major population centers without being absorbed into them...
I bet a lot of economists out there are leaping to the conclusion that conversion was discouraged to prevent subjects from escaping their tax burdens. But it turns out that this plausible story does not hold water:
Should tax status change on conversion? For the first eighty years or so of Arab rule the answer was generally no. The Arab aristocracy refused to sacrifice the cash cow that paid for the continuing expansion of the empire.