The Abbasid Revolution (ath-thawra al-ʿAbbāsiyya), also called the Movement of the Men of the Black Raiment (حركة رجال الثياب السوداء ḥaraka rijāl ath-thiyāb as-sawdāʾ), was the overthrow of the Umayyad Caliphate (661–750 CE), the second of the four major Caliphates in Islamic history, by the third, the Abbasid Caliphate (750–1517 CE). Coming to power three decades after the death of the Islamic prophet Muhammad and immediately after the Rashidun Caliphate, the Umayyads were an Arab empire ruling over a population which was overwhelmingly non-Arab. Non-Arabs were treated as second-class citizens regardless of whether or not they converted to Islam, and this discontent cutting across faiths and ethnicities ultimately led to the Umayyads' overthrow. The Abbasid family claimed descent from al-Abbas, an uncle of Muhammad.
The revolution essentially marked the end of the Arab exclusive Islamic Caliphate and the beginning of a more inclusive, multiethnic state in the Middle East. Remembered as one of the most well-organized revolutions during its period in history, it reoriented the focus of the Muslim world to the east.
By the 740s, the Umayyad Empire found itself in critical condition. A succession crisis in 744 led to the Third Fitna, which raged across the Middle East for three years. The very next year, al-Dahhak ibn Qays al-Shaybani initiated a Kharijite rebellion that would continue until 746. Concurrent with this, a rebellion broke out in reaction to Marwan II's decision to move the capital from Damascus to Harran, resulting in the destruction of Homs – also in 746. It was not until 747 that Marwan II was able to pacify the provinces; the Abbasid Revolution began within months.
Nasr ibn Sayyar was appointed governor of Khurusan by Hisham ibn Abd al-Malik in 738. He held on to his post throughout the war of succession, being confirmed as governor by Marwan II in the aftermath.
Khurusan's expansive size and low population density meant that the Arab denizens – both military and civilian – lived largely outside of the garrisons built during the spread of Islam.