Safavid conversion of Iran to Shia Islam

Following their rise to power in Iran in the 16th century, the Safavid dynasty initiated a campaign of forced conversion against the Iranian populace, seeking to create a new demographic environment in which Shia Islam would replace Sunni Islam as the nation's religious majority. Over the course of the next three centuries, the Safavids (who were Twelver Shias) heavily persecuted Sunni Muslims, Jews, Christians, and other religious groups, eventually transforming Iran into a spiritual bastion of Shia Islam. This process led to hostilities with Iran's Sunni-majority neighbours, most notably the Ottoman Empire. Additionally, the Safavid campaign sought to ensure Twelver dominance among Shia Muslims, particularly with regard to Zaydism and Ismaʿilism—each of which had previously experienced their own eras of sectarian dominance. Through their actions, the Safavids were able to establish the Shia sect as the official religion of their empire, marking a significant turning point in Islamic history, which had been universally dominated by the Sunni sect until that period. It also marked a significant turning point in Iranian history, having been the nation's first demographic change since the Muslim conquest of Persia in the 7th century.

As a direct result of the Safavid conversion campaign, the Shia sect of Islam remains dominant among the populations of Iran and Azerbaijan, with the latter having the world's second-largest percentage of Shia Muslims behind Iran itself.