In 1501, a fourteen-year-old named Ismail rode into Tabriz at the head of his Qizilbash warrior-disciples, seized power, and declared Twelver Shi'ism the state religion of Iran — a country that had been overwhelmingly Sunni for nine centuries. Ismail claimed descent from the Prophet and was revered by his followers as something close to divine; this Shah Ismail I founded a dynasty that would rule for more than two centuries. Within a generation, Iran was Shi'a, and has remained so ever since — the religious identity that still defines the modern Iranian state. The Safavid dynasty was the third of the gunpowder empires (Ottoman, Mughal, Safavid), and the one whose religious choices most decisively shaped contemporary Middle Eastern politics.
The Safavid imposition of Shi'ism was deliberate, top-down, and prolonged: with almost no native Shi'a clergy to draw on, the dynasty imported scholars from southern Lebanon's Jabal Amil and from Iraq, persecuted Sunni resistance, ritually cursed the first three caliphs, and fused religious authority to royal patronage in a way that gave Iranian Shi'ism a distinctively clerical-state character. The dynasty's original power, though, lay in the Qizilbash — Turkmen tribal cavalry who venerated the shah as a near-messianic figure; the central problem of Safavid history was taming these kingmakers. The geopolitical consequence was a permanent confessional border with the Sunni Ottoman Empire to the west; the catastrophic defeat at Chaldiran in 1514, where Ottoman muskets and cannon broke the Qizilbash cavalry, fixed a frontier fought across for two centuries — the line that still roughly marks the Iran-Iraq border. The empire reached its zenith under Shah Abbas the Great (1587–1629), who curbed the Qizilbash by building a standing army of ghulam slave-soldiers, mostly Caucasian Christians converted and loyal to the crown alone, and moved his capital to Isfahan. Culturally, Safavid Iran produced a flowering of Persian miniature painting, carpet weaving, and architecture; Isfahan, with its great square and tiled mosques, was one of the largest and most splendid cities in the world — its boast was that it was 'half the world' — the heart of a state that linked the silk trade from China to Venetian merchants and exchanged embassies with Habsburg Europe against their common Ottoman enemy. After Abbas, weaker shahs let the army and treasury decay, and in 1722 a band of Afghan invaders besieged and took Isfahan, ending Safavid rule in all but name.
The Sunni-Shi'a divide that structures contemporary Middle Eastern conflicts — the Saudi-Iranian rivalry, the Iraqi civil war, Hezbollah, the Syrian war's confessional dimension — is in significant part the long downstream of the Safavid decision: a sectarian fault line that Ismail's choice in 1501 opened and that no later ruler has closed. Iran's clerical regime since the 1979 revolution, in which Khomeini's doctrine of velayat-e faqih placed a jurist atop the state, is the latest expression of the state-clerical fusion the Safavids invented five centuries earlier.