A coalition of pious Muslims who wanted reform of the sinful Umayyads, Arabs who had been left out of the Umayyad aristocracy, and converts who had been left out of even the perks Arabs got finally came together in a successful push to rid Syria of the Umayyads. The money and manpower came from the far east, from Samarkand and all those places beyond the Oxus River.
The key figure in Khurasan was a man known as Abu Muslim; he was the Abbasid agent, but was probably a Persian who became a fanatical Shi’ite. He was able to rally enough fighting men to the cause that they could bring a large army west. It was a long journey and probably few of them got home again, so that was some serious commitment to the cause. Abu Muslim told them that they were fighting to put a special holy man of the Prophet’s family in power, but he didn’t say who it was. It’s likely that many of the fighters believed it would be a descendant of Ali. In 747, Abu Muslim’s Khurasani men took control of Merv, the garrison city on the border of Iran and Afghanistan. This allowed them to march across Iran.
In Iran, they picked up more support. Persian culture wanted to reassert its dominance, after a hundred years of repression by Arab invaders. They didn’t want to leave Islam, rather they could use the puritanical Abbasid cause to take back local control of their cities. Al-Hajjaj’s governorship of Iraq had included Iran in its repressive policies. Persians who had not converted to Islam were persecuted; temples were destroyed and Zoroastrian believers killed. Abu Muslim didn’t give any support to a non-Muslim religion, but he accepted their military and financial support in exchange for more home rule in the next regime.
Back in Syria, the Umayyads had been fighting each other, and there was a major earthquake. Marwan II was still in charge, but he had fewer fighting men than usual. Just like the Roman and Persian armies diminished by years of campaigning against each other, the Umayyad armies had been supporting one or another Umayyad until they, too, had diminished and were tired. Money was growing short, and of course as soon as Abu Muslim took over Merv, taxes from the far east stopped coming to Damascus. Additionally, the Berber revolt in North Africa and a Kharijite rebellion in Yemen took place around the same time.
In 749, Abu Muslim’s army besieged the new garrison town of Wasit in Iraq, the town where Hajjaj had decreed only Syrians could live. A lot of Umayyad forces were trapped in Wasit in the siege, while other Abbasid armies moved on. Arabs who had suffered at Umayyad hands joined them, making it easy to take Kufa.
In Kufa, Abbas’s great-grandson as-Saffah was declared the new Caliph. If they waited longer, some of their conspirators would agitate for a descendant of Ali, and in truth the heart of the conspiracy had always been set on the Abbasids. Marwan II met the invaders in battle, but he was defeated and had to flee to Egypt. The victors entered Syria and captured Damascus.
- Caliphate: The History of an Idea, by Hugh Kennedy