642 Muslims peacefully occupied Persia.
- Persians welcomed the deliverance promised by the invaders.
Cities that resisted such as Reyy, Susa and Sarakhs were conquered by force of arms.
644 Umar, the second Caliph, was killed by Abu Lo'lo, a Christian Persian slave, and Uthman succeeded him as third Caliph.Choice of Uthman over Imam Ali (A) stirred waves of discontent within the community of Muslims. As Uthman took over control, some Muslims designated themselves as Shia of Imam Ali (A)-supporter of Imam Ali (A)-who was continuing to live in the simple manner of Prophet Mohammad (S).
644 Uthman, a wealthy merchant from the rich and powerful Umayyad clan, was elected successor by a council named by Umar before his death.
Uthman continued the conquests that had steadily increased the size of the Islamic empire, but the victories now came at a greater cost and brought less booty in return.
Uthman distributed many of the provincial governorships to members of his family. Thus, much of the treasure received by the central government went to Uthman's family and to other provincial governors.
- Mu'awiya built a Syrian tribal army strong enough to repel a Byzantine attack.
- Mu'awiya followed a series of campaigns against the
Byzantines, which resulted in the capture of Cyprus.
- To maintain uniformity, copies of the Qur'an collected from all Muslim territory were compared and one standard version was released and redistributed.
651 Trying to seek refuge in one province after another,
Yazdgerd III was at last murdered near Merv. - Persia officially became a Muslim state.
652 Muslim armies continued to Khorasan.
Most of the Muslim victories took place under Caliph Uthman.
- Uthman appointed the Umayyads as governors of the occupied districts.
- Violations of peace terms were severely punished.
- People were forced to pay a toll tax and a land tax.
- The inhabitants of invaded lands were incorporated into Islamic society as protected foreigners.
At the time of conquest there was no immediate obligation for conversion. Very few examples of compulsory conversion are recorded. The new religion was far simpler than the 5assanian ritualistic Zoroastrianism. The inclination was to eliminate racial inequality and discrimination and to help the poor. This was a period of radical changes in Persian society.
653 Abu Sufyan, the influential Meccan merchant, died.
- Muslims made separate treaties with each town or district.
Tribute rather than conversion was the main immediate concern. Existing local tax structure and social order remained almost unchanged except for warriors.
654 Mu'awiya captured Rhodes in Greece.
655 Mu'awiya defeated the Byzantine navy off the coast of Lycia in Anatolia.
656 A group of rebels besieged Uthman in his home, and after several days of fighting he was killed.
Uthman's death marked the beginning of open religious and political conflicts within the Islamic community.
656 Imam Ali (A) was invited by the Muslims of Medina to accept the Caliphate. Reluctant, he agreed only after long hesitation.
Imam Ali (A)'s brief reign was beset by difficulties due mostly to the corrupt state of affairs he inherited.
Imam Ali (A) based his rule on the Islamic ideals of social justice and equality. His policy was a blow to the interests of the Quraysh aristocracy of Mecca who had grown rich in the wake of the Muslim conquests.
656 The Quraysh demanded that Imam Ali (A) bring the murderers of Uthman to trial, and when he rejected their request, a rebellion against him was instigated.
The leaders of the rebellion were Talha and Zubair, two prominent Meccans, along with A'isha, Mohammad (5)'s widow. This rebellion, known as the Battle of the Camel, was quelled. The engagement derived its name from the fierce fighting that centered around the camel upon which A'isha was mounted.
656 Mu'awiya, a kinsman of the slain Caliph Uthman, bore the duty of revenge.
Because Imam Ali (A) neglected to apprehend and punish Uthman's murderers, Mu'awiya regarded him as an accomplice to the murder and refused to acknowledge his Caliphate.
- Persians provided advisors to the Muslims.
657 Imam Ali (A) marched to the Euphrates border of Syria and engaged Mu'awiya's troops at the famous Battle of Siffin. Mu'awiya's guile turned near defeat into a truce. Resorting to a trick that played upon the religious sensibilities of Imam Ali (A)'s forces, he persuaded the enemy to enter into negotiations that ultimately cast doubt on the legitimacy of Imam Ali (A)'s Caliphate and alienated a sizable number of his supporters, who came to be known as Kharijites.
- The Kharijites under the leadership of Ibn Wahab were opposed  to Imam Ali (A).
658 The Battle of Nahrawan was fought between Imam Ali (A) and the Kharijites. Ibn Wahab and most of his followers were killed.
658 During the rebellion of the Kharijites, Mu'awiya took advantage ofImam Ali (A)'s difficulties in Iraq to send a force to seize control of Egypt.
658 Hormozan became a military advisor to the Muslims in Medina.
660 Muslims consolidated their rule in Persia.
661 Ali (A) was assassinated in Kufa by a Kharijite, Ibn Muljam.
661 Having held both Syria and Egypt, Mu'awiya, the commander of the largest force in Muslim Empire, had the strongest claim to the Caliphate.
Meanwhile many of the Imam Ali (AYs followers pledged their loyalty to Imam Ali (A)'s elder son, Imam Hassan (A). They considered Imam Hassan (A) to be the rightful heir to Mohammad (s)'s position of leadership.
661 Mu'awiya refused to acknowledge Imam Hassan (A) as Caliph and began to prepare for war.
Imam Hassan (A) dispatched a force to meet Mu'awiya and then himself headed a larger force. With little money left, Imam Hassan (A), was plagued by defections from his army. Although some of his followers resented it fiercely, he opened peace negotiations and later in the year abdicated the Caliphate to Mu'awiya.