The leader of this movement was the Persian general, Abu Muslim Marwazi, who rebelled against Umayyad rule and advance his cause step by step until he was able to overthrow the Umayyad government. Although this movement originated from a profound Shi’ite background and came into being more or less with the claim of wanting to avenge the blood of the Household of the Prophet, and although people were even asked secretly to give allegiance to a qualified member of the family of the Prophet, it did not rise directly as a result of the instructions of the Imams. This is witnessed by the fact that when Abu Muslim offered the caliphate to the sixth Imam in Medina he rejected it completely saying "You are not one of my men and the time is not my time."
Finally the Abbasids gained the caliphate in the name of the family of the Prophet and at the beginning showed some kindness to people in general and to descendants of the Prophet in particular. In the name of avenging the martyrdom of the family of the Prophet, they massacred the Umayyads, going to the extent of opening their graves and burning whatever they found in them.85 But soon they began to follow unjust ways of the Umayyads and did not abstain in any way from injustice and irresponsible action. Abu Hanifah, the founder of one of the four Sunni schools of law, was imprisoned by al-Mansur and tortured86Ibn Hanbal the founder of another school of law was whipped. The sixth Imam died from poisoning after much torture and pain. The descendants of the Holy Prophet were sometimes beheaded in groups, buried alive, or even placed within walls of government buildings under construction.
Harun al-Rashid, the Abbasid caliph, during whose reign the Islamic empire reached the apogee of its expansion and power, occasionally would look at the sun and address it in these words: "Shine wherever thou wilt, thou shalt never be able to leave my kingdom." On the other hand his armies were advancing in the East and West, on the other hand a few steps from the palace of the caliph, and without his knowledge, officials had decided on their own to collect tolls from people who wanted to cross the Baghdad bridge. Even one day when the caliph himself wanted to cross the bridge he was stopped and asked to pay the toll.
A singer, by chanting two lascivious verses, incited the passions of the Abbasid caliph, Amin, who awarded him three million dirhams. The chanter in joy threw himself at the feet of the caliph saying, "Oh, leader of the faithful! You give me all this money?" The caliph answered, "It does not matter. We receive money from an unknown part of the country."
The bewildering amount of wealth that was pouring every year from all corners of the Islamic world into the public treasury in the capital helped creating luxury and a mundane atmosphere. Much of it in fact was often spent for the pleasures and iniquities of the caliph of the time. The number of beautiful slave girls in the court of some of the caliphs exceeded thousands. By the dissolution of Umayyad rule and the establishment of the Abbasids, Shi’ism did not benefit in any way. Its repressive and unjust opponents merely changed their name.