Shah Ismail I

Shah Ismail I declared Twelver Shi'ism the state religion of Iran in 1501 upon conquering Tabriz, a population then predominantly Sunni. Enforcement combined exile, executions, and the killing of Sunni scholars in Tabriz with persuasion and simple generational succession; by the later Safavid period Sunni Islam had receded sharply in Iran's central provinces, though the process was gradual and regionally uneven rather than a single clean substitution.