Why did Sunni and Shia Muslims split?

The short version: the division began with a disagreement over leadership after Muhammad’s death in 632, not over belief. Over the next three centuries the two sides acquired different accounts of religious authority, different hadith, different law and different public rituals, until they were two communities. Much of today’s Sunni–Shia map was then drawn by states, above all the Safavids, who made Iran Shia from 1501. Majority What follows is that history step by step, what each tradition says about it, and where historians disagree.

Both traditions share the Qur’an, the prayers, the fast of Ramadan and the pilgrimage to Mecca. The differences are over who holds religious authority after the Prophet, and therefore over which reports of his words are trusted and how the law is derived from them.^[1] Consensus

632: a question the Qur’an did not answer

The Qur’an names no successor to Muhammad and sets out no procedure for choosing one. Consensus According to the Muslim tradition, when he died in June 632 the Medinan Helpers met to choose a leader of their own; ʿUmar and Abū Bakr hurried to the meeting and secured the leadership for Abū Bakr, an early convert and the father of Muhammad’s wife ʿĀʾisha. ʿAlī, Muhammad’s cousin and son-in-law, was absent, preparing the body for burial, and is reported to have delayed his oath of allegiance for some months.^[2]​^[3] Majority on the outline (§4).

The two traditions read this moment differently, and both readings are old:

• The Sunni account holds that the community rightly chose its leaders, and that Abū Bakr, ʿUmar, ʿUthmān and ʿAlī were, in that order, the four “rightly guided” caliphs.
• The Shia account holds that Muhammad had designated ʿAlī, above all at the pool of Ghadīr Khumm on the way back from his last pilgrimage, and that the choice of Abū Bakr set that designation aside.

Historians divide too. Wilferd Madelung argued from the early sources that Muhammad’s family had a strong claim, that Abū Bakr’s election deliberately passed it over, and that ʿAlī’s party saw it so from the beginning.^[3] Others read the same sources as a contest among the leading companions with no clear designation, and treat the doctrine of ʿAlī’s appointment as a later development of that dispute.^[4] Contested What historians cannot do is settle the question the traditions disagree on: the sources that report Ghadīr Khumm and the meeting of the Helpers were written more than a century later, by partisans of both sides (§0). Consensus

656–661: a civil war, and three parties

The dispute became a war in 656, when rebels from Egypt and Iraq killed the third caliph, ʿUthmān, in Medina and acclaimed ʿAlī. ʿAlī defeated ʿĀʾisha, Ṭalḥa and al-Zubayr at the Battle of the Camel near Basra; he then met Muʿāwiya, ʿUthmān’s kinsman and governor of Syria, at Ṣiffīn on the Euphrates in 657, where the fighting ended in an arbitration that did not restore his position. Some of his own followers rejected the arbitration and became the Khārijites, “those who went out”; one of them killed ʿAlī in Kufa in January 661, and Muʿāwiya became sole ruler.^[3]​^[4] Consensus on the events.

The parties of this war are the ancestors of the main divisions. The partisans of ʿAlī, the shīʿat ʿAlī, gave the Shia its name; the Ibāḍīs of Oman and North Africa trace their origin to a moderate branch of the Khārijites; and the majority who accepted the outcome, and later revered all four of the first caliphs, became the Sunnis.^[4] Consensus But in 661 these were political parties, not yet religious communities with distinct doctrines. Majority

680: Karbalāʾ

When Muʿāwiya died in 680, ʿAlī’s son al-Ḥusayn, the grandson of Muhammad through his daughter Fāṭima, refused to swear allegiance to Muʿāwiya’s son Yazīd and set out for Kufa, whose men had invited him to lead them. At Karbalāʾ, on the Euphrates, a government army surrounded his small company, cut it off from water and, on 10 Muḥarram 61 AH, 10 October 680, killed almost all of them.^[5]​^[6] Consensus on the event and its date (§5).

Karbalāʾ turned a political loyalty into a religious one. Within a few years Kufans who had failed to come to al-Ḥusayn’s aid called themselves “the penitents” and marched out to die; another revolt, in the name of a son of ʿAlī called al-mahdī, followed.^[6] Majority The death of the Prophet’s grandson at the hands of a caliph’s army became the central story of Shia devotion, commemorated every year on ʿĀshūrāʾ. The full story is in What happened at Karbala?

750–950: two communities take shape

The decisive changes came under the Abbasids (§6).

A Shia doctrine of authority. Around the sixth imam, Jaʿfar al-Ṣādiq (d. 765) of Medina, a body of teaching took shape: that God designates each imam through his predecessor, that the imam has a special knowledge of religion, and that the community owes its obedience to him rather than to any caliph. Marshall Hodgson argued that this was when the Shia became a sect in the full sense, a community defined by its own doctrine of authority.^[7] Majority

Branches. The succession after Jaʿfar divided his followers. Most followed his son Mūsā and the line after him; others followed his son Ismāʿīl, and became the Ismāʿīlīs, whose Fatimid caliphs ruled Egypt from 969.^[1]​^[8] Consensus The Zaydīs held that any qualified descendant of ʿAlī and Fāṭima who rose against injustice could be imam, and ruled in northern Yemen, with interruptions, until 1962.^[1] Consensus

The hidden imam. When the eleventh imam died in 874, the group that became the Twelvers held that he had a young son whom God had hidden. After about seventy years of agents carrying his letters, the “complete occultation” was declared in 941; the hidden imam is identified with the Mahdī who will return.^[9]​^[1] Majority on the reports; the existence of the son is a matter of faith on which historians cannot rule. In the imam’s absence, authority passed to scholars, which is why Twelver jurists came to hold an authority that Sunni scholars do not.

A named Sunni community. The phrase ahl al-sunna wa-l-jamāʿa, “the people of the Prophet’s practice and of the community”, came into use at the same time for those who rejected both the Shia imamate and the rationalist theology of the Muʿtazila. In the ninth century the traditionists around Aḥmad ibn Ḥanbal came to accept all four of the first caliphs, ʿAlī included, as rightly guided, the position that became the Sunni consensus.^[10]​^[11] Majority

Two communities in the streets. By the tenth century the division was public. In Baghdad in 963 the Shia Buyid ruler had the markets closed on ʿĀshūrāʾ, and mourners processed through the streets in black; Sunni counter-commemorations and riots between quarters followed.^[1]​^[4] Majority

When did the split become a split? Some historians date the decisive break to Karbalāʾ, Hodgson to the imamate doctrine of Jaʿfar’s time, others to the tenth century, when separate law, hadith and ritual made two communities visible.^[7]​^[1]​^[9] Contested on the date; Majority that it was a process over these centuries.

1501 onward: states draw the map

For most of Islamic history Shia Muslims were minorities under Sunni rulers, with exceptions such as the Fatimids and the Buyids. The map changed in 1501, when Shah Ismāʿīl took Tabriz and declared Twelver Shiism the religion of his new state, in a country that was then mostly Sunni. With jurists brought from Jabal ʿĀmil in what is now Lebanon, and through shrines, endowments and the rituals of Muḥarram, the Safavids made Iran Shia within about a century; the Ottoman–Safavid wars were fought partly as a war of religions (§9).^[12]​^[13]​^[14] Majority Iran’s Shia majority, and the long rivalry between a Shia Iran and its Sunni neighbours, date from these centuries, not from the seventh.

In 1979 the Iranian revolution created something new in Shia history: a state ruled by jurists in their own name, under Khomeini’s doctrine of the guardianship of the jurist. Most of the senior Shia jurists of the day rejected his version of it (§12).^[15] Majority Since 2003 the division has also become a line of conflict between states and their allies, which §13 describes without commentary. Political

How many Sunni and Shia Muslims are there?

Pew’s 2009 study, still the standard estimate, put Shia Muslims at 10–13 per cent of all Muslims and Sunnis at 87–90 per cent. Shia Muslims are majorities in Iran, Iraq, Azerbaijan and Bahrain, and large minorities in Lebanon, Pakistan, India and Yemen.^[16] Majority Many Muslims identify with neither: in Pew’s 2012 survey, “just a Muslim” was the majority answer in eight countries, among them Kazakhstan, Albania, Indonesia and Mali, and the most common answer in four more.^[17] Majority

Common misconceptions

• “Sunni and Shia have different Qur’ans.” They share the same text; the differences are over authority, hadith and law (§3 on the text’s history). Consensus
• “The split is a fourteen-century religious war.” For most of the history traced in this series, Sunnis and Shia lived side by side and often intermarried, and their rivalries were driven as much by states as by doctrine. Majority
• “It happened at once, in 632.” The disagreement began then; the two communities, with their own names, doctrines and rituals, took shape over the following three centuries. Majority
• “Shia Islam is Iranian.” Its early centres were in Kufa, Medina and Baghdad, among Arabs; Iran became mostly Shia only in the sixteenth century. Consensus

What the evidence cannot settle

Whether Muhammad designated ʿAlī is a question each tradition answers from its own reports, and those reports were written down long after the events by people already on one side. A historian can date the dispute, trace how each side’s doctrine developed, and show when states turned it into geography; the question of who was rightly entitled to lead is outside what the evidence can decide. Consensus