Three of Islam's first four caliphs were assassinated
In under thirty years after Muhammad's death in 632, the first caliphs carried a new state from Arabia to Egypt, Persia and the edge of Central Asia. Yet only Abu Bakr, the first, died of natural causes. Umar, Uthman and Ali were all killed, and the arguments over who should lead still divide Muslims today.
Sunni Muslims call these four leaders the Rashidun, the 'rightly guided', and treat their era from 632 to 661 as a golden age second only to the Prophet's own lifetime. The Arabic rāshid means one who has found the right path. Not everyone agrees on the list. Shia Muslims, some 10 to 15 percent of Muslims worldwide, recognise only Ali as a legitimate caliph and regard the first three as usurpers, while Ibadis accept only Abu Bakr and Umar. Even within Sunni tradition, the canon of four only settled after the ninth century.
Unlike the dynasties that followed, these caliphs were chosen by consultation among senior companions, called shūrā, or named by their predecessor. Kinship mattered: Abu Bakr and Umar were both Muhammad's fathers-in-law, and Uthman and Ali married his daughters. Abu Bakr secured the Arabian Peninsula; under Umar, from 634 to 644, the caliphate swallowed more than two-thirds of the Byzantine Empire and almost all of the Sasanian Empire. Uthman completed the conquest of Persia in 651.
Within its first 25 years the caliphate became the strongest economic and military power in West Asia and northeast Africa. By the 650s it held the Levant, parts of the Caucasus, North Africa as far as modern Tunisia, and lands from the Iranian Plateau into Central and South Asia.
Unity broke after Uthman's assassination in 656. Ali, Muhammad's cousin and son-in-law, moved the capital to Kufa, but Mu'awiya, Uthman's kinsman and governor of Syria, refused to recognise him until the killers were punished. The resulting civil war, the First Fitna, reached a stalemate at Siffin, and a faction called the Kharijites broke away over Ali's decision to accept arbitration. One of them killed Ali in 661. Mu'awiya then pressed Ali's son Hasan to abdicate and founded the Umayyad Caliphate.
Source: Rashidun Caliphate
