The Ottoman Empire was founded in 1299 by Osman I in northwestern Anatolia. It grew to be a powerful Sunni Islamic empire and caliphate under rulers like Murad I, Mehmed II, and Suleiman the Magnificent. Mehmed II conquered Constantinople in 1453, establishing Istanbul as the new capital and center of the Islamic world. In the 16th century, Suleiman expanded the empire significantly through his military campaigns in Europe and Asia. However, the empire began a slow decline in the late 16th century as its institutions and military failed to modernize. By the 19th century, the empire was weakened and faced defeats and invasions.