What happened
Protests grew through 1978 in escalating cycles: mourning processions after demonstrators were killed drew fresh crackdowns, with per-event casualty figures that vary widely. On 19 August 1978 the Cinema Rex fire in Abadan killed around 400 people behind locked doors (estimates range from about 377 to over 470) — the deadliest single event of the wave; later scholarship and the postrevolutionary trial attribute the arson to Islamist militants, though SAVAK was widely blamed at the time. The Jaleh Square shootings of 8 September 1978, remembered as Black Friday, hardened the movement, while strikes — above all in the oil industry — paralyzed the state and martial law failed. Khomeini, directing the movement from exile in Najaf and then Paris, became its symbol. The shah left Iran on 16 January 1979, and Khomeini returned on 1 February to crowds estimated in the millions. On 11 February 1979 the army declared neutrality and the monarchy collapsed.
Background
The standard list of causes includes autocracy and SAVAK repression, the grievance of the 1953 coup, oil-boom inflation and inequality, rapid Westernization that alienated religious society, and the organizing power of the clergy and its mosque networks. The opposition spanned Islamists, leftists, liberals, and bazaar merchants.
Consequences
A referendum approved the Islamic Republic in April 1979, and a new constitution established velayat-e faqih — rule of the Islamic jurist — with Khomeini as Supreme Leader. Rival revolutionary factions, liberal and leftist, were progressively pushed out, and rights organizations have documented executions numbering in the thousands in the post-revolutionary purges of the following years, with estimates varying. In November 1979 students seized the US embassy and held 52 American hostages for 444 days, breaking relations with the United States to this day. The revolution transformed regional politics and political Islam worldwide, and assessments of it remain deeply contested inside and outside Iran.