The Sunni-Shia Divide

An ancient religious divide is helping fuel a resurgence of conflicts in the Middle East and Muslim countries. Struggles between Sunni and Shia forces have fed a Syrian civil war that threatens to transform the map of the Middle East, spurred violence that is fracturing Iraq, and widened fissures in a number of tense Gulf countries. Growing sectarian clashes have also sparked a revival of transnational jihadi networks that poses a threat beyond the region.

Islam’s schism, simmering for fourteen centuries, doesn’t explain all the political, economic, and geostrategic factors involved in these conflicts, but it has become one prism through which to understand the underlying tensions. Two countries that compete for the leadership of Islam, Sunni Saudi Arabia and Shia Iran, have used the sectarian divide to further their ambitions. How their rivalry is settled will likely shape the political balance between Sunnis and Shias and the future of the region, especially in Syria, Iraq, Lebanon, Bahrain, and Yemen.

Alongside the proxy battle is the renewed fervor of armed militants, motivated by the goals of cleansing the faith or preparing the way for the return of the messiah. Today there are tens of thousands of organized sectarian militants throughout the region capable of triggering a broader conflict. And despite the efforts of many Sunni and Shia clerics to reduce tensions through dialogue and counterviolence measures, many experts express concern that Islam’s divide will lead to escalating violence and a growing threat to international peace and security.

Sunni and Shia Muslims have lived peacefully together for centuries. In many countries it has become common for members of the two sects to intermarry and pray at the same mosques. They share faith in the Quran and the Prophet Mohammed’s sayings and perform similar prayers, although they differ in rituals and interpretation of Islamic law.

Shia identity is rooted in victimhood over the killing of Husayn, the Prophet Mohammed’s grandson, in the seventh century, and a long history of marginalization by the Sunni majority. Islam’s dominant sect, which roughly 85 percent of the world’s 1.6 billion Muslims follow, viewed Shia Islam with suspicion, and extremist Sunnis have portrayed Shias as heretics and apostates.

Origins of the Schism

Mohammed unveiled a new faith to the people of Mecca in 610. Known as Islam, or submission to God, the monotheistic religion incorporated some Jewish and Christian traditions and expanded with a set of laws that governed most aspects of life, including political authority. By the time of his death in 632, Mohammed had consolidated power in Arabia. His followers subsequently built an empire that would stretch from Central Asia to Spain less than a century after his death. But a debate over succession split the community, with some arguing that leadership should be awarded to qualified individuals and others insisting that the only legitimate ruler must come through Mohammed’s bloodline.

A group of prominent early followers of Islam elected Abu Bakr, a companion of Mohammed, to be the first caliph, or leader of the Islamic community, over the objections of those who favored Ali ibn Abi Talib, Mohammed’s cousin and son-in-law. The opposing camps in the succession debate eventually evolved into Islam’s two main sects. Shias, a term that stems from shi’atu Ali, Arabic for “partisans of Ali,” believe that Ali and his descendants are part of a divine order. Sunnis, meaning followers of the sunna, or “way” in Arabic, of Mohammed, are opposed to political succession based on Mohammed’s bloodline.

Ali became caliph in 656 and ruled only five years before he was assassinated. The caliphate, which was based in the Arabian Peninsula, passed to the Umayyad dynasty in Damascus and later the Abbasids in Baghdad. Shias rejected the authority of these rulers. In 680, soldiers of the second Umayyad caliph killed Ali’s son, Husayn, and many of his companions in Karbala, located in modern-day Iraq. Karbala became a defining moral story for Shias, and Sunni caliphs worried that the Shia Imams—the descendants of Husayn who were seen as the legitimate leaders of Muslims (Sunnis use the term “imam” for the men who lead prayers in mosques)—would use this massacre to capture public imagination and topple monarchs. This fear resulted in the further persecution and marginalization of Shias.

Even as Sunnis triumphed politically in the Muslim world, Shias continued to look to the Imams—the blood descendants of Ali and Husayn—as their legitimate political and religious leaders. Even within the Shia community, however, there arose differences over the proper line of succession. Mainstream Shias believe there were twelve Imams. Zaydi Shias, found mostly in Yemen, broke off from the majority Shia community at the fifth Imam, and sustained imamate rule in parts of Yemen up to the 1960s. Ismaili Shias, centered in South Asia but with important diaspora communities throughout the world, broke off at the seventh Imam. Most Ismailis revere the Aga Khan as the living representative of their Imam. The majority of Shias, particularly those in Iran and the eastern Arab world, believe that the twelfth Imam entered a state of occultation, or hiddenness, in 939 and that he will return at the end of time. Since then, “Twelvers,” or Ithna Ashari Shias, have vested religious authority in their senior clerical leaders, called ayatollahs (Arabic for “sign of God”).

Many Christian, Jewish, and Zoroastrian converts to Islam chose to become Shia rather than Sunni in the early centuries of the religion as a protest against the ethnic Arab empires that treated non-Arabs as second-class citizens. Their religions influenced the evolution of Shia Islam as distinct from Sunni Islam in rituals and beliefs.

Sunnis dominated the first nine centuries of Islamic rule (excluding the Shia Fatimid dynasty) until the Safavid dynasty was established in Persia in 1501. The Safavids made Shia Islam the state religion, and over the following two centuries they fought with the Ottomans, the seat of the Sunni caliphate. As these empires faded, their battles roughly settled the political borders of modern Iran and Turkey by the seventeenth century, and their legacies resulted in the current demographic distribution of Islam’s sects. Shias comprise a majority in Iran, Iraq, Azerbaijan, and Bahrain, and a plurality in Lebanon, while Sunnis make up the majority of more than forty countries from Morocco to Indonesia.

Modern Tensions

Iran’s Islamic Revolution in 1979 gave Shia cleric Ayatollah Ruhollah Khomeini the opportunity to implement his vision for an Islamic government ruled by the “guardianship of the jurist” (velayat-e faqih), a controversial concept among Shia scholars that is opposed by Sunnis, who have historically differentiated between political leadership and religious scholarship. Shia ayatollahs have always been the guardians of the faith. Khomeini argued that clerics had to rule to properly perform their function: implementing Islam as God intended, through the mandate of the Shia Imams.

Under Khomeini, Iran began an experiment in Islamic rule. Khomeini tried to inspire further Islamic revival, preaching Muslim unity, but supported groups in Lebanon, Iraq, Afghanistan, Bahrain, and Pakistan that had specific Shia agendas. Sunni Islamists, such as the Muslim Brotherhood and Hamas, admired Khomeini’s success, but did not accept his leadership, underscoring the depth of sectarian suspicions.

Saudi Arabia has a sizable Shia minority of roughly 10 percent, and millions of adherents of a puritanical brand of Sunni Islam known as Wahhabism (an offshoot of the Sunni Hanbali school) that is antagonistic to Shia Islam. The transformation of Iran into an overtly Shia power after the Islamic revolution induced Saudi Arabia to accelerate the propagation of Wahhabism, as both countries revived a centuries-old sectarian rivalry over the true interpretation of Islam. Many of the groups responsible for sectarian violence that has occurred in the region and across the Muslim world since 1979 can be traced to Saudi and Iranian sources.

Saudi Arabia backed Iraq in the 1980–1988 war with Iran and sponsored militants in Pakistan and Afghanistan who were primarily fighting against the Soviet Union, which had invaded Afghanistan in 1979, but were also suppressing Shia movements inspired or backed by Iran.

The transformation of Iran into an agitator for Shia movements in Muslim countries seemed to confirm centuries of Sunni suspicions that Shia Arabs answer to Persia. Many experts, however, point out that Shias aren’t monolithic—for many of them, identities and interests are based on more than their confession. Iraqi Shias, for example, made up the bulk of the Iraqi army that fought Iran during the Iran-Iraq War, and Shia militant groups Amal and Hezbollah clashed at times during the Lebanese civil war. The Houthis, a Zaydi Shia militant group in Yemen, battled the government of Ali Abdullah Saleh, a Zaydi, several times between 2004 and 2010. Then, in 2014, the Houthis captured the capital Sana'a with ousted president Saleh's support.

For their part, both mainstream and hard-line Sunnis aren’t singularly focused on oppressing Shias. They have fought against coreligionists throughout history, most recently in the successive crackdowns on the Muslim Brotherhood in Egypt, Iraq’s 1990 invasion of Kuwait, and Saudi Arabia’s battles against al-Qaeda and related Sunni militant groups. Sharing a common Sunni identity didn’t eliminate power struggles among Sunni Muslims under secular or religious governments.

But confessional identity has resurfaced wherever sectarian violence has taken root, as in Iraq after the 2003 U.S.-led invasion removed Saddam Hussein, a dictator from the Sunni minority who ruled over a Shia-majority country. The bombing of a Shia shrine in Samara in 2006 kicked off a cycle of sectarian violence that forced Iraqis to pick sides, stirring tensions that continue today.

In the Arab world, Shia groups supported by Iran have recently won important political victories. The regime of Syrian President Bashar al-Assad, which has ruled since 1970, relies on Alawis, a heterodox Shia sect that makes up about 13 percent of Syria’s population, as a pillar of its power. Alawis dominate the upper reaches of the country's military and security services and are the backbone of the forces fighting to support the Assad regime in Syria’s civil war. Since the 2003 invasion of Iraq unseated Saddam Hussein and instituted competitive elections, the Shia majority has dominated the parliament and produced its prime ministers. Hezbollah, the Lebanese Shia militia and political movement, is the strongest party in Lebanon. The Houthis, Shia militants in Yemen tenuously linked to Iran, have toppled the country's internationally recognized government. Iran, a majority Shia country, has seen its regional influence swell as its allies in these countries have accumulated power.

Sunni governments, especially Saudi Arabia, have increasingly worried about their own grips on power, a concern that was exacerbated during the protest movement that began in Tunisia in late 2010. The Arab Awakening, as the uprisings are known, spread to Bahrain and Syria, countries at the fault lines of Islam’s sectarian divide. In each, political power is held by a sectarian minority—Alawis in Syria and a Sunni ruling family in Bahrain—where Shias are the majority. In Yemen, Houthi rebels have expanded their territorial control, which Saudi Arabia perceives as a potential beachhead for Iran on the Arabian peninsula, along vital shipping routes in the Red Sea and in territory abutting Saudi Arabia's own marginalized Shia minority.

Practicing the Faith

Sunnis and Shias agree on the basic tenets of Islam: declaring faith in a monotheistic God and Mohammed as his messenger, conducting daily prayers, giving money to the poor, fasting during the Muslim holy month of Ramadan, and performing the pilgrimage to Mecca.

There are divisions even over the precepts of Islam, but the main difference relates to authority, which sparked the political split in the seventh century and evolved into divergent interpretations of sharia, or Islamic law, and distinct sectarian identities.

Shias believe that God always provides a guide, first the Imams and then ayatollahs, or experienced Shia scholars who have wide interpretative authority and are sought as a source of emulation. The term “ayatollah” is associated with the clerical rulers in Tehran, but it’s primarily a title for a distinguished religious leader known as a marja, or source of emulation. Iran’s supreme leader, Ali Khamenei, was appointed by an elected body of Iranian clerics, while maraji (plural of marja) are elevated through the religious schools in Qom, Najaf, and Karbala. Shias can choose from dozens of maraji, most of whom are based in holy cities in Iraq and Iran. Many Shias emulate a marja for religious affairs and defer to Supreme Leader Ali Khamenei in Iran for political guidance. For Sunnis, authority is based on the Quran and the traditions of Mohammed. Sunni religious scholars, who are constrained by legal precedents, exert far less authority over their followers than their Shia counterparts.

Both sects have subdivisions. The divisions among Shias were discussed above. Four schools comprise Sunni jurisprudence: Hanafi, Shafii, Maliki, and Hanbali, the latter spawning the Wahhabi and Salafi movements in Saudi Arabia. Sunnism, a broad umbrella term for non-Shia Islam, is united on the importance of the Quran and practice of Mohammed but allows for differences in legal opinion.

Sectarian Militants

Violence between Islam’s sects has been rare historically, with most of the deadly sectarian attacks directed by clerics or political leaders rather than erupting spontaneously. Extremist groups, many of which are fostered by states, are the chief actors in sectarian killings today.

Two of the most prominent terrorist groups, Sunni al-Qaeda and Shia Hezbollah, have not defined their movements in sectarian terms, and have favored using anti-imperialist, anti-Zionist, and anti-American frameworks to define th