The civil war involved three main battles between the fourth Rashidun caliph, Ali, and the rebel groups.

Afterward, Mu'awiya, the incumbent governor of Syria, declared war on Ali, ostensibly to avenge Uthman's death.

After reasserting Muslim control over the dissident tribes of Arabia, he sent armies to fight against the empires of Byzantium and Sasanian Persia, initiating a wave of conquests which were continued by his successor Umar (r. 634–644).

These battles brought about the near-total collapse of the Sasanians, and restricted the Byzantine Empire to Anatolia, North Africa, and its holdings in Europe.

Provincial surplus was spent on the Muslim settlers of the conquered territories rather than forwarded to the capital, Medina.

He began centralizing power by relying on his Umayyad relatives, who had long opposed Muhammad before converting to Islam in 630.

[9] This was coupled with Arab nomads' antipathy toward central authority, which had hitherto been superseded by the continued war effort.

[10] The continued migration of tribes from Arabia to the conquered territories also resulted in reduced payments from the revenue of the lands, which led to resentment among the earlier settlers.

[12] Furthermore, Uthman took control of the crown lands of Iraq as state assets, and demanded that the provincial surplus be forwarded to the caliph.

This interference in provincial affairs brought about widespread opposition to his rule, especially from Iraq and Egypt, where the majority of the conquering armies had settled.

[13] Encouraged by the Medinese elite including prominent figures like Talha, Zubayr, Amr ibn al-As (a former governor of Egypt who Uthman deposed), and Muhammad's wife Aisha, the provincial opposition subsequently broadened into open rebellion.

[16] The rebels raised an army and captured Basra from Ali's governor, inflicting heavy casualties on his men, with the intention of strengthening their position.

Likely for the dishonorable act of leaving his fellow Muslims behind in a civil war he caused, Zubayr was pursued and killed by the troops of al-Ahnaf bin Qays, a chief of the Banu Sa'd who had remained on the sidelines of the battle.

[25] This pardon was also extended to high-profile rebels, including Marwan, who soon joined with his Umayyad kinsman Mu'awiya ibn Abi Sufyan, the governor of Syria, as a senior advisor.

[26] Shortly after assuming power, Ali dismissed most governors whom he considered corrupt, including Mu'awiya, Uthman's cousin.

[29] In response, Mu'awiya declared war on Ali on behalf of the Syrians, demanding vengeance for Uthman's death.

[42] Compelled by strong peace sentiments in his army and threats of mutiny, Ali accepted a proposal for arbitration.

[47] At Dumat al-Jandal, the arbitrators reached the verdict that Uthman had been killed wrongfully and that Mu'awiya had the right to seek revenge.

[51] The Kufan delegation reacted furiously to Abu Musa's concessions, and the erstwhile arbitrator fled to Mecca in disgrace.

[57] While Ali largely succeeded in regaining their support, the remaining opponents of arbitration gathered in Nahrawan, on the east bank of the Tigris.

[66] After multiple failed attempts at deescalation, Ali announced an amnesty (that did not apply to murderers) and barred his army from commencing hostilities.

[68] In January 661, while praying at the Mosque of Kufa, Ali was assassinated by the Kharijite Abd al-Rahman ibn Muljam.

These were facilitated by military commanders and tribal chiefs who had been swayed to Mu'awiya's side by promises and offers of money.