Abbasid Revolution was one of the most important events of medieval Islamic history. The Umayyad autocratic rule privileged Syrian Arab tribes and ignored ambitions of new converts to Islam. The initiative to the fall of Umayyad dynasty came from Shiite opposition organized by Hashimiya sect. The revolt of both Arabs and Iranian converts was led by Abu Muslim, who in 747 raised black flags of Abbasid dynasty in Khorasan. However, after the victory Abu Muslim himself was executed by his masters and Abbasid despotic rule was imposed on the Arab-Muslim Empire.