Complex sentence: Until the 15th century, most Persian Muslims were Sunni Muslims, though today Iran is known as a stronghold of the Shi'a Muslim faith, recognizing Islam as their religion and the prophet's son in law, Ali as an enduring symbol of justice.
Split into simpler sentences: Until the 15th century, most Persian Muslims were Sunni Muslims, though today Iran is known as a stronghold of the Shi'a Muslim faith. Recognizing Islam as their religion and the prophet's son in law, Ali as an enduring symbol of justice.