Who was the legitimate heir to the prophet Muhammad is a difficult question in Islam, an ongoing source of disagreement and conflict, and a formative moment in the history of the faith. The issue became especially important during the expansion of Islam and the nature of the political states this expansion created.
Emerging in fifth-century Arabia, Islam spread rapidly across the region under the leadership of the prophet Muhammad. Though he served as the leader of the faith from its founding until the end of his life, Muhammad never clearly appointed a successor. This gap lead to disagreements among the faithful over the future of Islam’s leadership, eventually leading to a schism between different groups of believers. This, in turn, shaped the political development of the regions into which Islam grew.
Death of Muhammad
The prophet Muhammad passed away in A.D. 632 in present-day Saudi Arabia. Nearly immediately, disagreements broke out over who should legitimately succeed him as the leader of the Muslim community. The prophet’s longtime friend and companion Umar nominated Abu Bakr, Muhammad’s senior companion and father-in-law. Others among Muhammad’s inner circle dissented and nominated Ali ibn Abi Talib, who was Muhammad’s cousin and son-in-law.
Hereditary succession was not an option because none of Muhammad’s sons lived into adulthood. According to the "Encyclopedia of Islam and the Muslim World," tensions between different camps grew, eventually culminating in violent conflict during the First and Second Fitnas, or Islamic Civil Wars, that cemented the split between Sunni and Shiite Islam which exists to the present day.
Sunnis and Shiites
Sunni Muslims are the spiritual descendants of the followers of Abu Bakr. Initially, they cited various hadith, or Islamic oral traditions, in which Muhammad recommended community discussions and voting as the best means for making group decisions. Arguing that Abu Bakr occupied a special place among the believers as the most prominent leader, the first male to convert to Islam and the prophet’s preferred second-in-command, they chose him as the rightful heir, or the first Caliph. In her book, "Islam, a Short History," Karen Armstrong notes that Sunni histories of the event go so far as to say that Ali eventually agreed that Abu Bakr should assume the role. However, these stories are roundly dismissed by Shiites.
Shiites, or followers of Shia Islam, believe that God alone can choose the successor to the prophet. Arguing that the other prophets -- including Abraham, Jesus and Muhammad -- were divinely chosen, they point to Quranic scripture, in particular the sura, or Quran chapter, called Al-Ma’ida, as a mandate for Ali. Armstrong notes that Shiites further support this with various hadith they claim refer directly to Ali, thus supporting their choice with Muhammad's own words.
Fate of an Empire
Despite violent conflict between believers during the Fitnas, the Islamic Caliphate remained relatively unified. Stretching from Spain across North African and into Central Asia, it was a large and powerful empire under which trade and culture flourished. However, with the fall of the Ummayad dynasty, the central government weakened and individual sultans and emirs became increasingly independent, eventually factionalizing into modern nation states. These new nations, in turn, became part of the split established following the death of Muhammad. Tensions still exist in the Muslim world between the predominantly Shia states -- including Iran, Iraq, Azerbaijan and Bahrain -- and the rest of the Middle East and North Africa. Within many Islamic nations, conflicts between Sunnis and Shiites are still the cause of violence and persecution of the minority group.