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 replace Sunni Islam, whose Shafi'i school of jurisprudence pervaded the country, as the denomination of the majority of the population. Over the course of three centuries, the Safavids (who were Twelver Shias) heavily persecuted Sunni Muslims, Jews, Christians, and other religious groups, eventually transforming Iran into a bastion of Shia Islam.

Source: Wikipedia — Safavid conversion of Iran to Shia Islam (CC BY-SA 4.0)