Charles Martel - The battle of tours

[Randarkmaan]

It's good that you mention the financial motive for many Arab rulers, because at first Islam was thought of primarily as an Arab religion, created by Arabs for the Arabs (Most of those who were converted to Islam during the early expansion were Arabs). The Arabs placed themselves as rulers over a large number of other peoples, the Arabs could identify themselves by being Muslim, while the majority of their subjects were not. As they had to pay the Jiziyah tax, the Arabs were therefore able to make more money off their non-Muslim subjects than they would if they were Muslims. This could be avoided by converting to Islam, something, the religion at least, encouraged, but many rulers tried to halt conversion among their non-Muslim subjects (for fear of losing the extra income that came with them) and in some cases when someone converted, they (the rulers) continued to demand that they pay as much tax as before. They did after all need a lot of money to pay soldiers and otherwise finance wars and other costly ventures.

Anyway it seems that many Christians hadn't necessarily been better off under the Byzantines than they were under the Arabs, as at the time it lost control of much of the Middle East the Byzantines had been taking hard measures against various "heresies" such as Monophysitic christians (I think Syrian christians, Egyptians and Armenians). And a not so nice treatment of Jews as well, I remember reading that many Jews outright supported their new Muslim overlords.

One of the main aims of the Abbassid revolution was to make Islam more universal, and to make sure that Non-Arab Muslims (especially Persians) were equal to Arab Muslims, as the Quran said they should be. Therefore conversion was more actively encouraged and usually not worked against during Abbasid rule, taxation was generally less severe over all also, you might say they were similar to the Victorians in that they wanted to "enlight the population of the world with the values of their religion and culture" (Protestant and British culture for the Victorians and Islam and Persian/Arabic culture for the Abbassids).

When the Abbassids declined and splintered to pieces the various new dynasties became, again, nearly invariably interested with extracting as much wealth from their people as possible to enrich themselves and to finance wars against their neighbours (who usually were Muslims, at least the ruelrs and the soldiers). Notable exceptions were the Caliphate of Cordoba (and many of the Taifa states) and the early Fatimid Caliphate of Egypt (the later period it was not much more than a military dictatorship).