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thumb|[[Imam Reza shrine, the holiest religious site in Iran, Mashhad]]
Islam is the official religion of Iran. Islam was introduced through the Arab conquest of Iran in the 7th century, which led to the fall of the Sasanian Empire and the gradual conversion of the Iranian population over several centuries. By the 10th century, most Persians had become Muslims, and Iranian dynasties and scholars played a major role in the development of Islamic civilization during the Islamic Golden Age.
Between the 7th and 15th centuries, Sunni Islam was the dominant sect in Iran. In the early 16th century, the Safavid dynasty established Twelver Shia Islam as the state religion through state-sponsored conversion campaigns, transforming Iran into a predominantly Shia country. Over the following centuries, Shia Islam became closely intertwined with Iranian identity and political culture.
Since the Iranian Revolution of 1979, Iran has been governed as an Islamic republic based on the doctrine of Guardianship of the Islamic Jurist (velayat-e faqih), with Shia Islam and the Ja'fari school designated as the official religion and basis of the legal system. Iran is today a predominantly Shia Muslim country, with Sunni Muslim minorities and smaller non-Muslim communities.
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