The dispute between the Sunni and Shiite Islamic sects was initially caused by the disagreements over the successor to the Prophet Muhammad after his death in 632 AD and over the nature of leadership in the Muslim community. The historical debate centred on whether to award leadership to a qualified, religious person who believed and would follow the customs of the Prophet or someone exclusively from the Prophet’s bloodline. Initially, the leaders settled the question by electing Abu Bakr a companion of the Prophet as the first Caliph (Arabic for “successor”). Even if most Muslims agreed with this decision, others supported Ali ibn Abi Talib, the Prophet’s cousin and son-in-law. Ali ibn Abi Talib was a husband of the Prophet’s daughter Fatima. Despite playing a prominent role during the Prophet’s lifetime, Ali lacked seniority within the Arabian tribal system as such he was bypassed. Ali’s followers did not approve of this decision because they regarded Abu Bakr and the two succeeding Caliphs (Umar and Uthman) to be illegitimate.

Ali’s followers believed that the Prophet Muhammad himself had named Ali as successor. Thus, the election of Abu Bakr was a violation of the divine order. A few of Ali’s partisans orchestrated the murder of the third Caliph Uthman in 656 AD, and Ali was named Caliph. However, he was assassinated in 661 AD, and his son Hussein (680 AD) died in battle against forces of the Sunni caliph. Shiite Muslims revered Ali’s eldest son Hassan (670 AD). Some of the Muslims claim that the Sunni caliph Muawiyah poisoned him. Ali’s supporters became known as “Shia,” a word derived from the term “Shi’a Ali,” meaning “supporters” or “helpers of Ali.” The group that respected and accepted the legitimacy of Ali’s caliphate but were against political succession based on bloodline to the Prophet came to be known as Sunni. This group constituted the majority of Muslims. “Sunni,” means the “followers of [the Prophet’s] customs [sunna]”.

The caliphate declined as a religious and political institution after the thirteenth century. However, the term “caliph” continued to be used by some Muslim leaders until Turkey’s first President Mustafa Kemal Ataturk abolished it in 1924. To some Sunni Islamic activists, the decline and abolition of the caliphate became an influential religious and political symbol in the nineteenth and twentieth centuries. These activists argued that leaders in the Islamic world had undermined the caliphate by abandoning the “true path” of Islam. Thus, Osama bin Laden and other contemporary Sunni extremists advocated for the restoration of a new caliphate established on “pure” Islamic principles. The socioeconomic, ethnic, linguistic, and religious diversity that exists within the global Muslim community present significant challenges to the re-emergence of centralised, pan-sectarian, and widely recognised Islamic religious leaders.

Over time, there is a political focus of the Sunni-Shia divide because each sect has developed into diverse communities and sometimes nations, each with a distinct nationalism. One overarching identity that continues to influence and classify the region is Muslim – Shia, Sunni, and Sufi– all practice in the birthplace of Islam in the Arabian Peninsula and broadly the Middle East and the world. During the time of Mohammad, Muslims practised together under a single leadership, but after the death of the Prophet, the Islamic leaders split. The recently formed states were critical to the modern manifestation of the Shi’a-Sunni Divide, in particular, the Islamic Republic of Iran and the Kingdom of Saudi Arabia after the Second World War.