A major part of the legacy of the Arab conquest was Shia Islam, which, although it has come to be identified closely with Iran, was not initially an Iranian religious movement. It originated with the Arab Muslims. In the great schism of Islam, one group among the community of believers maintained that leadership of the community following the death of prophet Mohammad rightfully belonged to Mohammad's son-in-law, Ali, and to his descendants. This group came to be known as the Shiat Ali, the partisans of Ali, or the Shias. Another group, supporters of Muawiya (a rival contender for the caliphate following the murder of Uthman), challenged Ali's election to the caliphate in 656. After Ali was martyred while praying in a mosque at Kufa in 661, Muawiya was declared caliph by conspiracy. He became the first caliph of the Umayyad dynasty, which had its capital at Damascus (Source: ICS).
Islamization of Persia in Seventh Century
