He lost control of the Golden Horde 1436, fled to Crimea, quarreled with the Crimeans, led a 3000-man army north and took the border town of Belyov. In 1437 Vasily II sent against him a huge army under the command of Dmitry Shemyaka, but they were defeated in the battle of Belyov. Soon after he moved to Volga and in 1438 captured Kazan, separating it from the Golden Horde.