Volga Bulgaria finally fell to the armies of the Mongol prince Batu Khan in the late 1230s (see Mongol invasion of Volga Bulgaria). The inhabitants, mixing with the Golden Horde's Kipchaks, became known as the "Volga Tatars". Another theory postulates that there were no ethnic changes in that period, and Bulgars simply switched to the Kipchak-based Tatar language. In the 1430s, the region again became independent as the base of the Khanate of Kazan, a capital having been established in Kazan, up the Volga from the ruined capital of the Bulgars.