Spread of Islam

• 1. Introduction

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  The spread of Islam turned a faith born in Mecca into the religion of one in four people alive today. By 2016, 1.7 billion people were Muslim, making Islam the world's second-largest religion. Nearly a third of all children born worldwide between 2010 and 2015 were born to Muslim families. That makes Islam the fastest-growing major religion on Earth. The scale took shape slowly, across almost 1,400 years. It began with the death of Muhammad in 632 CE and the conquests that followed. Armies carried the new faith outward from Mecca toward the Indian, Atlantic and Pacific Oceans. But armies cannot fully explain why so many different peoples eventually called themselves Muslim. What convinced a Zoroastrian, a Mongol khan or a Christian patriarch to change faith? And why did some regions convert within decades while others held out for centuries?

• 2. Terminology and Its Politics

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  Alongside the phrase 'spread of Islam', historians also use 'Islamization', 'Islamicization' and 'Islamification', written in Arabic as أسلمة. All three describe the same process: a society shifting until it becomes majority Muslim. That shift is not sudden. It has unfolded over centuries, region by region. The list runs from the Levant and Iran to North Africa and the Horn of Africa. It continues through West Africa and Central Asia, then into South Asian states such as Afghanistan, the Maldives, Pakistan and Bangladesh. Southeast Asia followed too, in Malaysia, Brunei and Indonesia. So did Southeastern Europe, in Albania, Bosnia and Herzegovina and Kosovo. Eastern Europe saw shifts in the Caucasus, Crimea and the Volga region. Southern Europe saw it in Spain, Portugal and Sicily, before Christian rule returned to each.

  In contemporary usage, 'Islamization' can carry a negative charge. Critics use it to describe an Islamist social and political system being imposed on a society with a different indigenous background.

  The English word 'Muslimization' has circulated since before 1940, appearing for instance in the Waverly Illustrated Dictionary. It carries a meaning close to 'Islamization'. More recently, it has also described the overtly Muslim practices that new converts adopt to reinforce a freshly acquired religious identity.

  That question of what pushed conversion forward, force or choice, runs through every century of the empire that followed.

• 3. Conquest Without Conversion

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  Within a single century of Islam's founding, Arab armies built a vast empire. It stretched from the Atlantic Ocean to the Aral Sea, and from the Atlas Mountains to the Hindu Kush. It was bounded, in one description, by 'a combination of natural barriers and well-organized states.' For the people living under this new empire, formerly subjects of Byzantium or Persia, daily life changed little at first. The conquest's real goal was practical: fertile land and water were scarce back in Arabia. Genuine religious conversion, on that account, only took hold generations later.

  The historian Ira M. Lapidus separated the era's converts into two distinct groups. One group were animists and polytheists from Arabian and Fertile Crescent tribes. The other were Christians and Jews who already lived under Byzantine or Sasanian rule before the Arabs arrived. For pastoral, tribal peoples, Lapidus wrote, conversion answered 'the need for a larger framework for political and economic integration, a more stable state.' For Christians, Jews and Zoroastrians already living under Byzantine or Sasanian rule, Islam simply replaced one political identity and religious affiliation with another. Conversion, at first, was neither required nor particularly wanted. As Lapidus put it, the conquerors were hostile to conversions because new Muslims diluted the economic and status advantages of the Arabs.

  The Umayyad caliphs opened the empire's first school, teaching Arabic and Islamic studies. They also began an ambitious mosque-building project across their territory. Many of those mosques still stand today, among them the Umayyad Mosque in Damascus. Yet by the end of the Umayyad period, fewer than one in ten people in Iran, Iraq, Syria, Egypt, Tunisia and Spain were Muslim. Only the Arabian Peninsula itself had a higher share of Muslims among its population.

• 4. The Long Curve of Conversion

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  The Abbasids dismantled the old, tightly-knit Arabian elite and its tribal politics. In its place spread a cosmopolitan culture: Islamic science, philosophy, theology, law and mysticism, alongside the gradual conversion of the empire's people. Similar conversions occurred beyond the empire's borders too. Turkic tribes in Central Asia and peoples south of the Sahara converted through contact with Muslim traders and Sufi orders.

  By the end of the 10th century, a large share of the population had converted. The British-Lebanese historian Albert Hourani offered one explanation. As he put it, Islam had 'become more clearly defined, and the line between Muslims and non-Muslims more sharply drawn.' Christians, Jews and Zoroastrians became known as 'People of the Book,' protected by treaty but subject to real restrictions. They paid a special tax, faced limits on the colors they wore, and could not marry Muslim women. Those rules elaborated on the Quran's basic guidance about non-Muslims, called dhimmis, who paid a separate tax instead of the zakat Muslims paid.

  The historian Ira Lapidus challenged an older assumption directly. 'It is now apparent,' he wrote, 'that conversion by force, while not unknown in Muslim countries, was, in fact, rare.' Muslim conquerors, he argued, wanted to dominate rather than convert, so most conversions were voluntary, blending worldly motives with spiritual ones. Lapidus also noted that most converts kept a deep attachment to their original cultures even after joining a new religious community. That mix, he pointed out, still shows up in the diversity of Muslim societies today.

  The scholar Richard Bulliet's 'conversion curve' put the Umayyad-era conversion rate for non-Arab subjects at just 10 percent. Under the Abbasids, that changed. Bulliet estimated Muslim numbers grew from about 40 percent in the mid-9th century to nearly the whole population by the 11th century's end. Other estimates push the timeline later still. Muslims may not have been a majority in Egypt until the mid-10th century, or in the Fertile Crescent until 1100. What is now Syria may have kept a Christian majority until the Mongol invasions of the 13th century. Early on, becoming Muslim meant formally joining an Arab tribe as a client, called a mawali. Around 930, a new law required every bureaucrat in the empire to be Muslim. Economic hardship, social disorder and pressure from Muslim attackers also drove the forced mass conversion of the Samaritans during this Abbasid period.

  None of this explains how Islam reached people the caliphate's armies never conquered at all: traders and preachers who never fought a battle.

• 5. Trade Routes and Holy Men

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  In Africa, Islam moved along three distinct routes. One crossed the Sahara and Sahel through trading towns such as Timbuktu. A second ran up the Nile Valley through Sudan and reached as far as Uganda. A third crossed the Red Sea and traveled down the East African coast through settlements like Mombasa and Zanzibar.

  Early Muslims once fled to the port city of Zeila, in modern Somaliland, seeking the protection of the Aksumite Emperor in present-day Ethiopia. Some of those refugees settled across the Horn region and helped spread the faith there. After Muslims defeated the Quraysh in the 7th century, Arabian trading partners had all adopted Islam themselves. Trade then carried the religion into Somali coastal cities, reinforced by later waves of migrating Muslim families.

  By the 10th century, Ali ibn al-Hassan Shirazi, one of seven sons of a ruler of Shiraz in Persia, founded the Kilwa Sultanate. His mother was an Abyssinian slave girl, and after his father died his brothers drove him out of his inheritance. His successors built the most powerful sultanate on the Swahili coast, stretching at its peak from Inhambane in the south to Malindi in the north. The 13th-century traveler Ibn Battuta described the great mosque of Kilwa Kisiwani as built entirely of coral stone, the only such structure in the world.

  Shared language and shared religion gave Arab and West African traders across the Sahara and Sahel a reason to trust and invest in one another. Toward the 19th century, the Sokoto Caliphate, led by Usman dan Fodio in northern Nigeria, pushed the spread of Islam further still. In Central Asia, the Samanids, starting in the 9th century, spread Sunni Islam and Persian culture as far as Taraz, in what is now Kazakhstan. Under their rule, the Quran received its first complete Persian translation.

  Muslim sailors reached the shores of Indonesia before Islam had even taken root there, arriving from the Abbasid ports of Basra and Debal. The earliest Muslim gravestone in the region dates to 1082. When Marco Polo visited in 1292, he found the port of Peureulak already Muslim. Chinese records describe a Muslim delegation reaching the emperor from the Kingdom of Pasai in 1282. The Sultanate of Malacca began after ruler Parameswara Dewa Shah converted and took the name Muhammad Iskandar Shah upon marrying a daughter of Pasai's ruler. In 1380, Sufi orders carried Islam onward to Mindanao. In Java, the Hindu Majapahit Empire's court took on a Muslim character even before its own ruler converted. That ruler, Raja Kertawijaya, converted in 1475 at the hands of the Sufi sheikh Rahmat.

  In Jerusalem, that same religion would arrive by four-month siege rather than by camel caravan.

• 6. Jerusalem, Iberia and the Balkans

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  In November 636, the Rashidun caliph Umar's forces began the siege of Jerusalem against the Byzantines. For four months the siege continued. The city's Greek Orthodox patriarch, Sophronius, an ethnic Arab, ultimately agreed to surrender in person. Umar traveled from Medina and signed the terms himself in the spring of 637. Sophronius negotiated what became known as Umar's Assurance, granting Christians religious freedom in exchange for the jizya tax. When his prayer time came inside the Church of the Holy Sepulchre, Umar refused to pray there. He feared future Muslims might use his prayer as an excuse to seize the church. So the Mosque of Umar was built facing its doors instead. Later caliphs in Damascus, and then in Baghdad, stayed largely tolerant of their Christian subjects. Harun Abu Ja'far, who ruled from 786 to 809, even sent the keys of the Holy Sepulchre to Charlemagne. That tolerance narrowed once the Fatimid Caliphate, ruled from Cairo, took Palestine in the 9th century. Around 969, Jerusalem's patriarch, John VII, was executed for corresponding with the Byzantines. Decades later, the sixth Fatimid caliph, al-Hakim bi-Amr Allah, destroyed the Holy Sepulchre in 1009. That act helped ignite the fury behind the First Crusade.

  Tariq ibn Ziyad led the Islamic conquest of Visigothic Hispania from 711 to 718, and Gibraltar still carries his name, from the Arabic Jabal Tariq. His mostly-Berber army had conquered the peninsula's southern and central regions by 720. Arab forces even pushed into southern France, holding the old province of Septimania around Narbonne, before Charles Martel stopped their advance at Poitiers. In 750, a fleeing Umayyad prince who escaped a massacre in Damascus reached Cordoba and founded a new Islamic state there. Centuries of reconquest followed: victory at Covadonga in 722, Toledo retaken in 1085, and the Battle of Las Navas de Tolosa in 1212. Valencia fell to James I of Aragon in 1238, Cordoba to Ferdinand III in 1236, and Seville soon after in 1248. Granada, the last Muslim kingdom, fell in 1492 to Isabelle of Castile and Ferdinand of Aragon. By 1499, the remaining Muslims were ordered to convert or leave, and many who stayed hid their practices from the Spanish Inquisition.

  In Belgrade, the number of mosques fell from more than 70 in 1750 to just three by 1850. Ottoman conquest there was primarily military and economic, not religious. The empire's millet system let Christian communities keep their own laws and leaders. Catholic regions such as Bosnia, Kosovo and northern Albania saw more conversions than Orthodox ones, partly from suspicion of loyalty to the Papacy. After Austria defeated the Ottomans in 1699, many Balkan Muslim converts chose to leave for territory still under Ottoman rule.

  Further east, the Mongols would destroy the caliphate itself before eventually adopting its religion.

• 7. Persia and the Mongol Conversion

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  Older historians once argued that Zoroastrianism collapsed quickly once the Sassanid Empire fell to the Islamic conquest of Persia, between 632 and 654 CE. That model assumed the religion was too tightly bound to the fallen state to survive. Some conversions did happen en masse: the Sassanid army division at Hamra converted before the Battle of al-Qadisiyyah. Still, conversion actually moved fastest in garrisoned urban areas, leaving Zoroastrianism increasingly associated with the countryside. By the end of the Umayyad period, Muslims remained only a minority in the region. Not until the 16th century did most people in what became Iran and Azerbaijan adopt Shia Islam, under Safavid conversion policies.

  Zoroastrian purity law treated fire-related trades as defiling, so workers in industrial and artisan jobs converted to Islam readily. The historian Thomas Walker Arnold noted how easily a Zoroastrian could translate Ahura Mazda and Ahriman into Allah and Iblis. Muslim leaders sometimes encouraged attendance at prayer with promises of money, and let the Quran be recited in Persian rather than Arabic.

  The Mongols besieged and destroyed Baghdad in 1258, ending the caliphate and, at first, persecuting Islam in favor of Buddhism. Then, in 1295, the Ilkhanate's new khan, Ghazan, converted to Islam himself. Two decades later the Golden Horde's Uzbeg Khan, who lived from 1282 to 1341, followed suit, reportedly converted by the Sufi Saint Baba Tukles. Berke Khan had already become the first Mongol monarch to adopt Islam. He even opposed his relative Hulagu Khan to help defend Jerusalem at the Battle of Ain Jalut in 1263. A Franciscan friar, William of Rubruck, visited Batu Khan's camp in the 1240s. He wrote, 'I wonder what devil carried the law of Machomet there.'

  That same Mongol-Islamic fusion would go on to shape the spread of Islam across Central Asia and into the Indian subcontinent.

• 8. Islam in the Modern World

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  The Ottoman sultanate was abolished on the 1st of November 1922, and the caliphate itself followed on the 3rd of March 1924. With it, the political center that had anchored Muslim identity for centuries disappeared. Modern-day Islamization looks different: individuals returning to Muslim values, communities and dress codes, and reinforcing community from within. The French researchers Gilles Kepel and Olivier Roy call this newer trend transnational Islam. It reflects what they describe as a 'growing universalistic Islamic identity' shared by Muslim immigrants and their children in non-Muslim countries. Better communication, media, travel and migration made a single, shared Islam imaginable everywhere, one that crosses national and ethnic lines. That global identity rarely means organized politics. The real center of Muslim religious life, one description notes, stays local: worship, discussion, charity and mutual aid.

  The 1980s and 1990s brought major conflicts, including the Arab-Israeli conflict, the wars in Afghanistan, and three separate Gulf Wars in 1980-88, 1990-91 and 2003-2011. Those conflicts internationalized what had been local disputes. Leaders such as Osama bin Laden and Abdallah Azzam became central to that shift, shaped as much by domestic and world politics as by religion.

  Across Africa, Muslims grew from 34.5 million in 1900 to 315 million in 2000. That raised their share of the continent's population from roughly 20 percent to 40 percent. Christians grew even faster in the same period, from 8.7 million to 346 million, overtaking Islam's growth rate on the continent.

  Since the 1960s, large numbers of Muslims have migrated to Western Europe as immigrants, guest workers, asylum seekers, or through family reunification. That migration has pushed Europe's Muslim population steadily upward. A Pew Forum study, published in January 2011, forecast Muslims rising from 6 percent of Europe's population in 2010 to 8 percent by 2030. That 2030 horizon is the point the spread is still moving toward.