The Safavids were a Shi'a brotherhood that took power in Iran in the 1400s and established Shi'a Islam as the dominant religion, shaping modern Iran. They were constantly at war with the neighboring Sunni Ottomans over control of the Fertile Crescent. Shah Abbas ruled during the Safavid Golden Age in the 1500s-1600s and rebuilt Isfahan, borrowing from various cultures to blend Persian arts and Shi'a Islam. However, weak later rulers led to military losses and the dynasty's fall by 1722, though it left a lasting cultural legacy.