In 632 CE, the Prophet Muhammad, the founder of Islam and leader of the first Muslim community formed through his preaching and military victories, passed away. However, before his death, he gave no clear instructions about who should succeed him. This immediately led to conflict among his followers, who were divided into two main factions: a majority that believed the successor should be elected based on specific tribal criteria, and a minority that viewed Ali, Muhammad’s cousin and son-in-law, as the only rightful heir.

The majority group became known as the "Sunnis," meaning "followers of the Sunnah", the collection of the Prophet’s practices and traditions. They chose Abu Bakr, a close friend of Muhammad, as the first Caliph, thereby making him the political leader of the Muslim community. On the other hand, the supporters of Ali came to be known as "Shiites" (from the Arabic shi'at, meaning "party" or "faction").

What began as a political dispute gradually evolved into deep theological divisions. For example, Sunnis regard the Quran as a flawless text that must be followed literally. Shiites, however, believe it requires interpretation by mujtahids, Islamic legal and religious scholars.

One of the most significant differences lies in the concept of the Imam. In Sunni Islam, the Imam is primarily a religious figure who leads prayer. In Shia Islam, the Imam is both a spiritual and political leader, a successor to Ali (and thus Muhammad), believed to be divinely appointed by God.

Today, Shiites make up about 10–15% of the global Muslim population. Despite being a minority, their presence and influence are far from diminished. The Sunni-Shia rivalry, fueled by centuries of theological and political divergence, continues to shape relations between Muslim-majority nations, such as Iran (the world's leading Shia power) and Saudi Arabia (one of the most staunchly Sunni states), both vying for dominance in the Middle East.

It can thus be said that the original dispute over Muhammad’s succession remains one of the most consequential episodes in Islamic history, still driving conflict, and at times, even outright hostility, between the two major branches of the faith.