The Battle of the Zab (Arabic: معركة الزاب), also referred to in scholarly contexts as Battle of the Great Zāb River, took place on January 25, 750, on the banks of the Great Zab in what is now the modern country of Iraq. It spelled the end of the Umayyad Caliphate and the rise of the Abbasid Caliphate, which would last from 750 to 1258.
The Abbasid revolution (Arabic: اَلثَّوْرَة اَلْعَبَّاسِيَّةِ, romanized: aṯ-Ṯawra al-ʿAbbāsiyyah), was the overthrow of the Umayyad Caliphate (661–750), the second of the four major caliphates in Islamic history, by the third, the Abbasid Caliphate (750–1517).
The Abbasid revolt originated in the eastern province of Khorasan in the mid-8th century, fueled by widespread discontent with Umayyad rule. The Abbasids, claiming descent from Muhammad's uncle Abbas, capitalized on various grievances, including discrimination against non-Arab Muslims (mawali), heavy taxation, and perceived impiety of Umayyad rulers. Led by Abu Muslim Khorasani, Abu Muslim's army composed largely of Arab settlers disillusioned with Umayyad rule, marched under black banners, forming a powerful force that swept westward in open revolt, defeating Umayyad forces. The decisive Battle of the Zab in 750 saw the Abbasid army triumph over the last Umayyad caliph, Marwan II. This victory led to the fall of the Umayyad dynasty and the establishment of Abbasid rule, marking a significant shift in the caliphate's power base from Syria to Iraq and ushering in a new era of Islamic governance.
The Great Zab or Upper Zab (Arabic: الزَّاب الْكَبِيْر, romanized: ez-Zâb el-Kebîr; Kurdish: Zêy Badînan or Zêyê Mezin; Turkish: Zap; Syriac: ܙܒܐ ܥܠܝܐ, romanized: zāba ʻalya) is an approximately 400-kilometre (250 mi) long river flowing through Turkey and Iraq. It rises in Turkey near Lake Van and joins the Tigris in Iraq south of Mosul. During its course, the river collects water from many tributaries and the drainage basin of the Great Zab covers approximately 40,300 square kilometres (15,600 sq mi). The river and its tributaries are primarily fed by rainfall and snowmelt – as a result of which discharge fluctuates highly throughout the year. At least six dams have been planned on the Great Zab and its tributaries, but construction of only one, the Bekhme Dam, has commenced but was halted after the Gulf War.
The Zagros Mountains have been occupied since at least the Lower Palaeolithic, and Neanderthal occupation of the Great Zab basin has been testified at the archaeological site of Shanidar Cave. Historical records for the region are available from the end of the third millennium BCE onward. In the Neo-Assyrian period, the Great Zab provided water for irrigation for the lands around the capital city of Nimrud. The Battle of the Zab – which ended the Umayyad Caliphate – took place near a tributary of the Great Zab, and the valleys of the river provided shelter for refugees from the Mongol conquest of Iraq. During the 19th and 20th centuries, the Great Zab basin saw frequent uprisings of local Kurdish tribes striving for autonomy.