What distinguishes Sunni and Shia Islam?

The distinction between Sunni and Shia Islam primarily stems from a historical disagreement over who should lead the Muslim community following the death of the Prophet Muhammad. This disagreement originated in the early days of Islam, specifically concerning the legitimacy of authority and leadership. Sunnis believe that the community should select the leader (caliph), which they support through historical precedents such as the selection of Abu Bakr as the first caliph. In contrast, Shia Muslims hold that leadership should remain within the Prophet's family, specifically believing that Ali, the Prophet's cousin and son-in-law, was divinely appointed to lead.

This fundamental divide set the foundation for differing beliefs, practices, and cultural traditions that evolved over centuries, leading to the formation of two major branches within Islam. While other aspects, such as interpretations of the Quran, styles of prayer, and dietary rules, may further distinguish the two groups, they largely stem from, or are influenced by, the initial leadership dispute. Therefore, the disagreement over succession is at the core of what distinguishes Sunni from Shia Islam.