In 1206 the new powerful military-feudal Mongolian state headed by Genghis Khan started the war of conquest against his neighbors. In 1223 in the battle near the Kalka river 25,000 Tatar-Mongols won a crushing victory over the squads of Southern Rus Princes, who were unable to come together even in the face of grave danger. Under the leadership of Batu, Genghis Khan's grandson, from 1237-1238, they conquered Riazan, Volodymir, Suzdal, and Yaroslavl lands.