The Third Fitna (Arabic: الفتنة الثاﻟﺜـة; al-Fitna al-thālitha), was a series of civil wars and uprisings against the Umayyad Caliphate beginning with the overthrow of Caliph al-Walid II in 744 and ending with the victory of Marwan II over the various rebels and rivals for the caliphate in 747. However, Umayyad authority under Marwan II was never fully restored, and the civil war flowed into the Abbasid Revolution (746–750) which culminated in the overthrow of the Umayyads and the establishment of the Abbasid Caliphate in 749/50. Thus a clear chronological delimitation of this conflict is not possible.
The civil war began with the overthrow of al-Walid II (743–744), the son of Yazid II (r. 720–724). Al-Walid had been designated by his father as the successor of the latter's brother, Hisham ibn Abd al-Malik (r. 724–743), and although his accession had initially been well received due to Hisham's unpopularity and his decision to increase army pay, the mood quickly changed. Al-Walid is reported to have been more interested in earthly pleasures than in religion, a reputation that may be confirmed by the decoration of the so-called "desert palaces" (including Qusayr Amra and Khirbat al-Mafjar) that have been attributed to him. His accession was resented by some members of the Umayyad family itself, and this hostility deepened when al-Walid designated his two underage sons as his heirs and flogged and imprisoned his cousin, Sulayman ibn Hisham. Further opposition arose through his persecution of the Qadariyya sect, and through his implication in the ever-present rivalry between the northern (Qaysi and Mudari) and southern (Kalbi and Yemeni) Arab tribes. Like his father, al-Walid was seen as pro-Qays, especially following his appointment of Yusuf ibn Umar al-Thaqafi as governor of Iraq, and the torture and death of Yusuf's Yemeni predecessor, Khalid al-Qasri. It must be noted though that adherence was not clear cut, and men from both sides of the divide joined the other.
In April 744, Yazid III, a son of al-Walid I (r. 705–715), entered Damascus. His supporters, bolstered by many Kalbis from the surrounding region, seized the town and proclaimed him caliph. Al-Walid II, who was at one of his desert palaces, fled to al-Bakhra near Palmyra. He mustered a small force of local Kalbis and Qaysis from Hims, but when Yazid III's far larger army under Abd al-Aziz ibn al-Hajjaj ibn Abd al-Malik arrived, most of his adherents fled. Al-Walid II was killed, and his severed head sent to Damascus. A pro-Qaysi uprising in Hims followed, under the Sufyanid Abu Muhammad al-Sufyani, but its march on Damascus was decisively defeated by the released Sulayman ibn Hisham. Abu Muhammad was thrown into prison in Damascus along with al-Walid II's sons.
During his brief reign, Yazid showed himself an exemplary ruler, modelling himself on the pious Umar II (r. 717–720). He was favourably disposed to the Qadariyya, and consciously tried to disassociate himself from the frequent criticism of autocratic rule levelled at his Umayyad predecessors. Thus he promised to refrain from abuses of his power—mostly concerning widespread resentment at heavy taxation, the enrichment of the Umayyads and their adherents, the preference given to Syria over other parts of the Caliphate, and the long absence of soldiers on distant campaigns—and insisted that not only was he chosen by the community in an assembly (shura), rather than appointed, but that the community had the right to depose him if he failed in his duties or if they found someone more fit to lead them. At the same time, his reign saw the renewed ascendancy of the Yemenis, with Yusuf ibn Umar dismissed and imprisoned after trying, without success, to raise the Qaysis of Iraq into revolt. Yusuf's successor in Iraq and the East was the Kalbi Mansur ibn Jumhur, but he was soon replaced by the son of Umar II, Abdallah ibn Umar ibn Abd al-Aziz. During his brief tenure, Mansur tried to dismiss the governor of Khurasan, Nasr ibn Sayyar, but the latter managed to maintain his post. Yazid died in September 744 after a reign of barely six months. Apparently due to the advice of the Qadariyya, he had appointed his brother, Ibrahim, as his successor, but he did not enjoy much support and was immediately faced with the revolt of Marwan II (r. 744–750), the grandson of Marwan I (r. 684–685) and governor of Upper Mesopotamia.
Marwan, who had for several years supervised the campaigns against the Byzantine Empire and the Khazars on the Caliphate's northwestern frontiers, had reportedly considered claiming the caliphate already at the death of al-Walid II, but a Kalbi rebellion in his rear had forced him to turn back. Yazid III appointed him to Upper Mesopotamia, and Marwan installed himself in the Qays-dominated city of Harran.