1. The Succession Dispute After Muhammad’s Death (632)

When Muhammad died in 632, he left no clear instructions about who should lead. His companions chose Abu Bakr, an early convert and his father-in-law, as the first caliph (“successor”). Some disagreed: they believed leadership belonged to Ali, Muhammad’s cousin and son-in-law through his daughter Fatima. Ali’s supporters were called “Shiat Ali” — the party of Ali — the origin of the word Shia.

At this stage the quarrel was purely political. Both sides prayed the same way and shared the same beliefs. There was no “Sunni” group yet either; most Muslims simply accepted whoever ruled. Ali himself served under the first three caliphs before becoming the fourth in 656.

2. The Conquests, the Civil War, and the Umayyad Empire (632–750)

The first four caliphs — Abu Bakr, Umar, Uthman, Ali — are known as the Rashidun, the “rightly guided.” In under thirty years their armies conquered Persia (modern Iran and Iraq), plus Syria, Palestine, and Egypt from the Byzantines. Three things made this possible: Byzantium and Persia had exhausted each other in decades of war; taxes under the new rulers were often lighter than before; and Christians, Jews, and Zoroastrians could keep their religions in exchange for a special tax. Many conquered populations were indifferent or even welcoming.

The conquests created a Muslim-ruled empire, not a Muslim population. For centuries, Muslims were a small ruling minority. Conversion came slowly, driven less by force than by advantage — escaping the tax, access to careers, intermarriage. Egypt and Syria probably had no Muslim majority until two or three centuries after conquest.

The succession dispute turned violent. Uthman was assassinated in 656. Ali’s rule was contested by Muawiya, governor of Syria and a relative of Uthman, in a civil war. In 661 Ali was assassinated — by a third faction angry at both men — and Muawiya took power.

Muawiya founded the Umayyad dynasty, moved the capital to Damascus, and made the caliphate hereditary. Umayyad armies reached Spain in 711 and pushed east to Central Asia and the edge of India — one of the largest empires the world had seen. But two grievances built up. In 680, Umayyad forces massacred Ali’s son Husayn — Muhammad’s grandson — with his family at Karbala in Iraq. And the Umayyads ruled as an Arab aristocracy: non-Arab converts faced discrimination and higher taxes. Together these fueled a massive revolt.

3. The Abbasid Golden Age (750–900s)

The revolt won in 750, but not for Ali’s side. Its slogan — rule for “the chosen one from the family of Muhammad” — turned out to mean the Abbasids, descendants of Muhammad’s uncle. They had ridden the anger of Ali’s partisans to power, then crushed Ali’s actual descendants once they had it. They massacred the Umayyad family and built a new capital: Baghdad, founded 762.

The early Abbasid era was Islam’s golden age. Baghdad was perhaps the largest, richest city in the world — possibly near a million people when European cities held tens of thousands. The caliphs funded translation of Greek, Persian, and Indian science and philosophy into Arabic, and Muslim scholars made lasting advances in mathematics (“algebra” comes from an Arabic book title), medicine, astronomy, and optics. Europe later rediscovered much ancient knowledge through these translations.

The same era built the religion’s real machinery — which never belonged to the caliphs. Religious authority rested with the ulama, scholars who developed Islamic law (sharia) from the Quran and the Prophet’s recorded practice; among Sunnis this produced four schools of law that still exist. Alongside them grew Sufism, Islam’s mystical strand, later organized into brotherhoods. This is why the caliphate could be captured and eventually destroyed without the religion collapsing: the religion never ran through the caliph.

4. How the Sunni-Shia Split Became a Religious Divide (680–950)

During these same centuries, the dispute over Ali changed from a political faction into a separate religion within Islam.

Karbala in 680 was the emotional turning point: the state’s killing of the Prophet’s grandson gave Ali’s cause a permanent core of martyrdom, still mourned yearly on Ashura. The Abbasid betrayal of 750 made clear that Ali’s line would never rule. The doctrinal break came in the 700s–900s, when Shia scholars developed the Imamate: the belief that God had designated a line of infallible Imams descended from Ali and Fatima, and that recognizing them was a matter of faith. This was a different theory of religious authority, not just a preference about rulers. In 874 the twelfth Imam disappeared as a child; mainstream Shia hold that he went into hiding and will return as a savior — the “Twelver” form practiced in Iran today.

Sunni identity formed largely in reaction: a mainstream built on the Prophet’s recorded practice, acceptance of all four first caliphs (whom Shia reject as usurpers), and community consensus rather than an infallible Imam. By around 950 the two were recognizably separate communities with distinct law, theology, and ritual. Calling the earlier conflicts — like Ali versus Muawiya — “Sunni versus Shia” projects later categories onto what was, at the time, a fight over power.

5. Islam Spreads Beyond the Caliphate: Spain, Africa, and the Trade Routes

One Umayyad prince, Abd al-Rahman, escaped the 750 massacre and seized power in Spain in 756. In 929 a descendant declared himself caliph too, so the Muslim world briefly had three rival caliphs: the Abbasid in Baghdad, the Umayyad in Cordoba, and the Fatimid in Cairo. Muslim Spain shrank over centuries under the Christian Reconquista until Granada, the last Muslim state, fell in 1492.

Armies were not the main way Islam spread in the long run — trade was. Across the Sahara it moved with the gold caravans into West Africa: the empire of Mali, whose king Mansa Musa’s 1324 pilgrimage reportedly depressed gold prices in Egypt, made Timbuktu a center of scholarship. Across the Indian Ocean, merchants and Sufi preachers carried Islam to India, East Africa, and Southeast Asia. No caliph’s army ever touched Indonesia, which today has the world’s largest Muslim population. Most Muslims now live in places no Arab empire ever ruled.

6. The Collapse: Slave Soldiers, Crusaders, and Mongols (900s–1400)

Abbasid power rotted from within. By the 900s, North Africa and Egypt had broken away — most importantly to the Fatimids, the Shia dynasty that founded Cairo in 969. In Baghdad, the caliphs had created their own problem: they bought Turkish boys from the Central Asian steppe and trained them as elite slave soldiers, valued because they had no local ties and answered only to the ruler. The institution worked too well — the slave soldiers became the only real army in the capital, and their generals came to control the caliphs who owned them. Persian warlords followed, then the Seljuk Turks, free tribesmen who took over most of the Middle East in the 1000s and kept the caliph as a figurehead.

Into this fragmented world came the Crusades. In 1099, European knights took Jerusalem and set up Christian states along the Mediterranean coast. To Europe this was an epochal holy war; to most Muslims at the time, a regional nuisance — and Muslim disunity let the crusader states survive nearly two centuries. Saladin, a Kurdish general, united Egypt and Syria, founded the Ayyubid dynasty, and retook Jerusalem in 1187.

Saladin’s dynasty relied on the same slave-soldier system as Baghdad — and in 1250, its Turkish slave corps in Egypt overthrew its masters and took power directly. This regime is known simply by the word for what its members had been: the Mamluks, Arabic for “owned.”

Then came the Mongols. In 1258, Hulagu, a grandson of Genghis Khan, sacked Baghdad, killed the last reigning Abbasid caliph, and wrecked the region for centuries. Two years later, at Ayn Jalut in Palestine, the Mamluks stopped the Mongol advance — the first force ever to do so. The Middle East split in two along that line. The Mongols kept Persia and Iraq, and within a few generations their rulers converted to Islam. The Mamluks kept Egypt and Syria for over 250 years, housing a powerless Abbasid “caliph” in Cairo for legitimacy, and expelled the last crusader strongholds in 1291. Around 1400 the region was devastated once more by Timur, a Central Asian conqueror of Mongol heritage whose enormous empire barely outlived him.

7. The Three Gunpowder Empires: Ottomans, Safavids, Mughals (1300–1700s)

Three great Muslim empires rose from the post-Mongol wreckage, their power resting partly on cannons and firearms.

The Ottoman Empire, founded by Turkish warriors in Anatolia around 1300, took Constantinople in 1453 — ending the thousand-year Byzantine Empire — and went on to rule the Balkans, the Middle East, and North Africa. After the Ottomans conquered Mamluk Egypt in 1517, a later legend claimed the last Abbasid formally handed them the caliphate; in reality the sultans wore the title loosely and only pushed the claim in the 1700s–1800s, when a weakening empire needed the prestige. Under Suleiman the Magnificent in the 1500s they besieged Vienna and dominated the Mediterranean.

The Safavid dynasty took Persia in 1501 and made Shia Islam the state religion by force — a deliberate political decision, and the reason Iran is Shia today while its neighbors are mostly Sunni. It locked the Safavids into centuries of war with the Ottomans along a sectarian border that still roughly matches the modern map.

The Mughal Empire was founded in India in 1526 by Babur, descended from both Genghis Khan and Timur. It ruled a huge Hindu majority as a Muslim minority, managed by its best emperors through alliance and tolerance. Its economy was among the world’s largest in the 1600s — the Taj Mahal is a Mughal tomb. The British East India Company absorbed the empire piece by piece in the 1700s.

8. Colonialism and the End of the Caliphate (1800s–1924)

European colonialism dismantled or dominated all three empires through the 1800s and early 1900s. In 1924, the new secular Republic of Turkey abolished the caliphate — ending the institution begun with Abu Bakr in 632. The religion continued without it, as it always had, carried by scholars, mystics, merchants, and believers, most of them living far from the old Arab heartlands.