The 1979 revolution that overthrew Mohammad Reza Shah and replaced a secular monarchy with an Islamic Republic under Ayatollah Khomeini — the first modern revolution to install religious governance, the event that redefined political Islam globally, and the origin point of the conflict architecture that has shaped the Middle East ever since.
Every major theory of revolution predicted Iran would not happen. Marxists expected revolutions from below by the working class against capitalism. Modernization theorists expected that economic development would produce secular, stable democracies. The Iranian Revolution was led by a clerical establishment, united a coalition of leftists, liberals, and Islamists against a modernizing pro-Western monarchy, and produced a theocratic republic that its most important participants — the secular left — had not wanted and did not survive. It broke every model. Understanding why is still one of the central problems of political science.