World Religions › Medieval › Islam
Sunni and Shia split
Succession dispute 632; Karbala 680· Event· Judaism, Christianity & Islam
Historical recordConfirmed by archaeology, outside sources or contemporary records.
Islam's main division, which began as a dispute over who should lead the Muslim community after Muhammad's death in 632.
See it on the World Religions map →What it is
When Muhammad died, leading Muslims chose his companion and father-in-law Abu Bakr as caliph; Sunnis accept him and the next caliphs as rightful. A minority held that Muhammad had named his cousin and son-in-law Ali, and that leadership belonged to his family: the Shia, from Shiat Ali, 'party of Ali.' Ali became the fourth caliph in 656 but was assassinated in 661. Over centuries the split grew into distinct law schools, rituals and religious leadership.
Why it matters
About 85–90% of Muslims are Sunni and 10–15% Shia, who are majorities in Iran, Iraq, Bahrain and Azerbaijan; the divide still shapes Middle East politics.
Sources and history
Early Arabic histories such as al-Tabari's, drawing on Sunni and Shia reporters; Shia claims rest especially on Muhammad's sermon at Ghadir Khumm, which both sides interpret differently.
Questions and debates
Whether Muhammad designated Ali, and what he meant at Ghadir Khumm, is the core disagreement; historians also debate when 'Sunni' and 'Shia' hardened into separate identities.
Inside this (1)
Connections (3)
▸Sunni and Shia split began over leadership of Caliphates: Rashidun, Umayyad, AbbasidHistorical record
The connection
The split began as a question about the caliphate itself: should the community choose its leader, as Sunnis hold it rightly did with Abu Bakr, or should leadership pass within Muhammad's family through Ali, as Shia believe? Ali's contested caliphate (656–661) brought civil war, and Umayyad rule pushed his supporters into opposition.
When and where
Medina, 632, where Abu Bakr was chosen at the Saqifa meeting; the First Fitna, or civil war, 656–661, including the battle of Siffin (657).
Historical evidence
Early Arabic histories such as al-Tabari's describe the Saqifa meeting and the civil war in detail, drawing on reporters with differing sympathies.
Questions and debates
How much the earliest dispute was religious versus tribal and political is debated; the Shia theology of the imams developed over the following centuries.
▸Battle of Karbala and the death of Husayn deepened Sunni and Shia splitHistorical record
The connection
Husayn's killing by a caliph's army turned a dispute over leadership into a sacred story of martyrdom. Mourning for Husayn, through Ashura passion plays, processions and pilgrimage to his tomb, became the heart of Shia identity, while Sunnis honor Husayn but do not center their faith on his death.
When and where
Karbala, Iraq, 680; the first organized mourners, the 'Penitents' (Tawwabun), rose in 684–685; Baghdad's rulers made Ashura mourning public in 963.
Historical evidence
Shia devotional literature from the 700s on, chronicles of Ashura mourning in Baghdad in 963, and today's mass rituals in Iraq, Iran, Lebanon and South Asia.
Questions and debates
Scholars debate whether Karbala created Shia identity or deepened one already forming around loyalty to Ali's family.
▸Iranian Revolution sharpened Sunni and Shia splitMostly agreed by scholars
The connection
The 1979 revolution created a Shia-led Islamic republic that sought to export its revolution, alarming Sunni-led Gulf monarchies, above all Saudi Arabia. The rivalry fed proxy conflicts in Iraq, Lebanon, Syria, Bahrain and Yemen, where political and sectarian lines often coincided, though both sides also claimed to speak for all Muslims.
When and where
Iran, 1979, then across the Middle East: the Iran–Iraq War (1980–88), Lebanon's Hezbollah (1982), Iraq after 2003, Syria and Yemen from 2011.
How do we know?
Diplomatic records, leaders' speeches, and studies of Iranian support for Shia groups and Saudi funding for Sunni ones document the rivalry.
Questions and debates
Many scholars argue the rivalry is mainly geopolitical, with sectarian identity used as a tool, rather than a revival of a 1,400-year-old religious feud.