Zoroastrianism
Conversion

Though subject to a new leadership and harassment, the Zoroastrians were able to continue their former ways, although there was a slow but steady social and economic pressure to convert, with the nobility and city-dwellers being the first to do so, while Islam was accepted more slowly among the peasantry and landed gentry. "Power and worldly-advantage" now lay with followers of Islam, and although the "official policy was one of aloof contempt, there were individual Muslims eager to proselytize and ready to use all sorts of means to do so."

In time, a tradition evolved by which Islam was made to appear as a partly Iranian religion. One example of this was a legend that Husayn, son of the fourth caliph Ali and grandson of Islam's prophet Muhammad, had married a captive Sassanid princess named Shahrbanu. This "wholly fictitious figure" was said to have borne Husayn a son, the historical fourth Shi'a imam, who insisted that the caliphate rightly belonged to him and his descendants, and that the Umayyads had wrongfully wrested it from him. The alleged descent from the Sassanid house counterbalanced the Arab nationalism of the Umayyads, and the Iranian national association with a Zoroastrian past was disarmed. Thus, according to scholar Mary Boyce, "it was no longer the Zoroastrians alone who stood for patriotism and loyalty to the past." The "damning indictment" that becoming Muslim was un-Iranian only remained an idiom in Zoroastrian texts.

With Iranian support, the Abbasids overthrew the Umayyads in 750, and in the subsequent caliphate government—that nominally lasted until 1258—Muslim Iranians received marked favor in the new government, both in Iran and at the capital in Baghdad. This mitigated the antagonism between Arabs and Iranians but sharpened the distinction between Muslims and non-Muslims. The Abbasids zealously persecuted heretics, and although this was directed mainly at Muslim sectarians, it also created a harsher climate for non-Muslims.
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