Most Kurds converted to Islam between the 7th and 9th centuries CE. The exact process of their religious conversion is unknown, but Kurds probably wanted to free themselves from the jizya, a tax on people who were not Muslims. Most became part of Sunni Islam, and most were Shafi'ites. The Kurds fought against the government at some times, but fought with the government's army at other times. Kurdish tribes made rebellions against the Rashidun Caliphate in 645 and in 659. In 666 there were two rebellions (in Ahvaz and in Fars). During the Umayyad Caliphate, Kurds made rebellions in 685, 702, and 708. Kurdish tribes fought for Marwan II (who controlled the Umayyad Caliphate) against the rebellion in 746.