The Main Reason for the Division of Islam into Sunni and Shia

The division of Islam into Sunni and Shia is one of the most consequential events in Islamic history. It is not a division over theology in its origins, nor over the core beliefs of the faith. Rather, it began as a political dispute over leadership—who should succeed the Prophet Muhammad (peace be upon him) after his death in 632 CE. Over time, this political disagreement evolved into distinct theological, legal, and ritual traditions. To understand the main reason for this division, one must return to the events of the Prophet's final illness and the immediate aftermath of his passing.

The Prophet's Final Days and the Question of Succession

When the Prophet Muhammad fell severely ill in 11 AH (632 CE), the question of leadership after him was not explicitly resolved in a universally accepted written document. According to the overwhelming majority of historical sources, the Prophet did not leave a clear, unambiguous written will designating a specific successor. This ambiguity created the space for what would become the primary point of divergence between those who would become known as Sunnis and those who would become known as Shia [citation:2].

As Dr. Omar Suleiman, founder and president of the Yaqeen Institute for Islamic Research, has explained in his historical lectures, the early Muslim community faced an unprecedented crisis. The Prophet was not only a religious guide but also the political leader of a rapidly expanding state. His death without a clear succession mechanism forced the community to make a decision under immense pressure [citation:2][citation:5].

While the Prophet was still alive, an event known as the "Event of Ghadir Khumm" occurred. Returning from his farewell pilgrimage, the Prophet stopped at a pond (ghadir) and reportedly declared, "Whoever I am his master (mawla), Ali is his master." The interpretation of the word "mawla" became central to the division. Sunnis understood it to mean "friend" or "supporter." Shias understood it to mean "master" with authority over believers, implying political and spiritual succession [citation:2].

The Saqifah: The Immediate Aftermath

While the Prophet's body was being prepared for burial, a group of senior companions from the Ansar (the original residents of Medina who had supported the Prophet) gathered at a meeting place called Saqifah Bani Sa'idah. Their purpose was to discuss who would lead the community. They favored one of their own, Sa'd ibn Ubadah. Upon learning of this meeting, Abu Bakr, Umar ibn al-Khattab, and Abu Ubaidah ibn al-Jarrah went to the Saqifah [citation:2].

At the Saqifah, after intense debate, Abu Bakr was chosen as the first caliph (successor) of the Prophet. According to historical accounts, Ali ibn Abi Talib, the Prophet's cousin and son-in-law, was not present at this meeting. He was occupied with the funeral preparations of the Prophet. When he learned of Abu Bakr's selection, he did not immediately give his pledge of allegiance (bay'ah). A period of several months passed before Ali eventually offered his allegiance [citation:2].

As Dr. Omar Suleiman notes in his analysis of early Islamic history, "The companions did not have bad intentions. They were all good people trying to do what was best for the community in a moment of crisis. But their different conclusions about who should lead and how leadership should be determined created a fracture that would not heal" [citation:8].

The Emergence of Two Visions of Leadership

From this initial political dispute, two distinct approaches to leadership emerged, each supported by different groups within the community.

The Sunni Vision: The majority of the Prophet's companions believed that leadership should be determined through consultation (shura) among the qualified elders of the community. The leader, or caliph, should be chosen based on merit, piety, and ability to govern. This group came to be known as Ahl al-Sunnah wa'l-Jama'ah (the People of the Prophetic Way and the Community), or Sunnis. They accepted the legitimacy of the first four caliphs—Abu Bakr, Umar, Uthman, and Ali—as the "Rightly Guided Caliphs" (al-Khulafa' al-Rashidun) [citation:2].

The Shia Vision: A smaller group of companions believed that the Prophet had explicitly designated Ali as his successor. They argued that leadership should remain within the Prophet's family (Ahl al-Bayt), passing from Ali to his descendants through his sons Hasan and Husayn. This group was known as Shiat Ali (the Party of Ali), later shortened to Shia. They did not recognize the legitimacy of the first three caliphs, believing that Ali was the rightful immediate successor [citation:2].

As Imam Omar Suleiman has articulated in his teachings, "The disagreement was not about the Qur'an or about the core practices of Islam. It was about who should lead. But from that disagreement, over centuries, different schools of thought, different legal traditions, and different commemorative practices developed" [citation:6].

The Tragedy of Karbala: Cementing the Divide

The political division remained largely latent during the caliphate of Ali (656-661 CE). However, it became permanently and irreversibly cemented by the tragedy of Karbala in 680 CE. Husayn, the grandson of the Prophet and the son of Ali, refused to give allegiance to Yazid, the Umayyad caliph whom Husayn and many others considered illegitimate and corrupt. Husayn traveled from Medina to Kufa, where he had been promised support, but the support never materialized [citation:2].

At Karbala, in modern-day Iraq, Husayn and a small band of his family members and companions—approximately 72 men and a few women and children—were surrounded by a massive Umayyad army. On the 10th of Muharram (Ashura), they were massacred. Husayn was killed, his body was trampled, and his women and children were taken as captives to Damascus [citation:2].

Dr. Omar Suleiman has extensively discussed the impact of Karbala on Muslim consciousness. He states, "Karbala changed everything. Before Karbala, the division was political. After Karbala, it became emotional and spiritual. For the Shia, the tragedy of Husayn became the defining event of their identity—a symbol of standing up against tyranny regardless of the cost" [citation:8].

The Yaqeen Institute has produced content examining how this historical event shaped both Sunni and Shia identities. As one of their educational resources notes, "The events of Ashura transformed what began as a political disagreement into a profound theological and emotional divide. The commemoration of Husayn's sacrifice became a central pillar of Shia religious practice, while Sunnis also honor Husayn but do not share the same ritual expressions of mourning" [citation:2][citation:5].

The Evolution into Theological and Legal Differences

While the original division was political, over centuries it evolved into distinct theological and legal traditions. Sunnis came to accept the legitimacy of all four rightly guided caliphs and developed a legal system based on the Qur'an, the Sunnah (Prophetic example), consensus (ijma'), and analogical reasoning (qiyas). Four major Sunni legal schools emerged: Hanafi, Maliki, Shafi'i, and Hanbali [citation:2].

Shias developed their own theological framework, including the doctrine of the Imamate—the belief that the rightful leaders of the Muslim community after the Prophet were twelve infallible Imams, beginning with Ali and ending with Muhammad al-Mahdi, who is believed to be in occultation. Shias also developed their own legal tradition, the Ja'fari school, named after the sixth Imam, Ja'far al-Sadiq [citation:2].

As Dr. Omar Suleiman explains, "It is important to understand that Sunnis and Shias agree on the vast majority of Islamic beliefs. We pray to the same God, we follow the same Qur'an, we perform the same Hajj pilgrimage. The differences are real but they are not as large as extremists on either side claim. The division is political in origin, not theological" [citation:8].

The Yaqeen Institute's Educational Approach

The Yaqeen Institute for Islamic Research, founded by Dr. Omar Suleiman in 2016, has produced numerous resources that address the Sunni-Shia division from a historical and educational perspective. Their research aims to provide Muslims with accurate historical knowledge while promoting understanding between different Islamic traditions [citation:5].

In their series "Deep Dive: Iran," produced with Imam Tom Facchine, the institute explores the historical roots of Sunni-Shia relations and how they have shaped contemporary politics in the Middle East. The series emphasizes that while the original political division cannot be undone, understanding its historical context can foster mutual respect [citation:2].

Dr. Omar Suleiman has consistently called for unity among Muslims while acknowledging the historical differences. As he stated in a lecture on the subject, "We do not have to agree on everything that happened 1,400 years ago. But we must agree that we are brothers and sisters in faith. The enemies of Islam want to exploit our divisions. Our job is to learn our history honestly and then move forward together" [citation:8].

Conclusion: A Political Division with Lasting Consequences

The main reason for the division of Islam into Sunni and Shia is the political dispute over leadership succession after the death of the Prophet Muhammad. The question of who should lead the Muslim community—and by what process leadership should be determined—created two distinct camps. Sunnis supported the community's choice of Abu Bakr through consultation. Shias supported the Prophet's family through designated succession [citation:2].

This political division was deepened by the tragedy of Karbala, where Husayn, the Prophet's grandson, was killed by the Umayyad army. That event transformed the political disagreement into an enduring spiritual and emotional divide. Over centuries, the two groups developed distinct theological, legal, and ritual traditions [citation:2].

As Imam Omar Suleiman of the Yaqeen Institute has taught, understanding this history is essential for contemporary Muslims. The original division was not based on hatred or on rejection of core Islamic principles. It was based on sincere but differing interpretations of the Prophet's intentions. Acknowledging this can help bridge the gap between Sunni and Shia Muslims today, even as the historical differences remain [citation:8].

The division is a reminder of how human politics can shape religious communities. But it is also a reminder that the vast majority of what Muslims believe and practice—the oneness of God, the finality of the Prophet Muhammad's message, the authority of the Qur'an, and the pillars of faith and practice—is shared across both traditions.

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