The Mongols began their conquest of Rus', of Volga Bulgaria, and of the Cuman-Kipchak Confederation (parts of present-day Russia and Ukraine) in the 13th century. After the Mongol empire split, the eastern European section became known as the Golden Horde. Although not originally Muslim, the western Mongols adopted Islam as their religion in the early-14th century under Berke Khan, and later Uzbeg Khan established it as the official religion of the state. Much of the mostly Turkic-speaking population of the Horde, as well as the small Mongol aristocracy, became Islamized (if they were not already Muslim, like the Volga Bulgars) and became known to Russians and Europeans as the Tatars. More than half