The Battle of the Zab on January 25, 750, marked the end of the Umayyad Caliphate and the beginning of the Abbasid dynasty, lasting until 1517. Facing the Umayyad Caliph Marwan II were the Abbasids, alongside Shia, Khawarij, and Iraqi forces. Despite the Umayyad army's numerical superiority and experience, its morale was low following previous defeats. The Abbasid forces, on the other hand, were highly motivated.

During the battle, the Abbasids employed a spear wall tactic, effectively countering the Umayyad cavalry's charge. The Umayyad army was decisively defeated, leading to a chaotic retreat with many soldiers either killed by the pursuing Abbasids or drowned in the Great Zab River. After the battle, Marwan II fled across the Levant but was eventually killed in Egypt. His death and the victory of the Abbasids ended Umayyad dominance in the Middle East, establishing Abbasid rule with Saffah as the new caliph.