The leaders of these troops were Chépé and Subutai Bahadar. The Polovtsi applied for help to the Russian prince Mstislav Mstislavitch, and he called together the princes of southern Russia, amongst whom the most important were Mstislav Romanovitch of Kiev and Mstislav Sviatoslavitch of Tchernigov. The armies of the princes moved to the help of the Polovtsi, and although the Tatars sent ambassadors saying, “God has permitted us to come on our steeds with our slaves against the accursed Polovtsi; come and make peace with us, for we have no quarrel with you,” the princes decided upon a battle which took place by the river Kalka in the government of Iekaterinoslav. The Russian princes, who did not act in unison, were beaten (1223), and many were killed, amongst others Mstislav of Kiev. The Tatars did not penetrate far into Russia, but turned back and were soon forgotten.[12] Meanwhile the Tatar captains returned to Jenghiz Khan, who, having definitively subdued Tangut and northern China, died in 1227. He had during his lifetime divided his possessions amongst his four sons: to the descendants of Juji (then already dead) was allotted Kiptchak (that is the steppe extending from central Asia into southern Russia); to Jagatai, Turkestan; to Okkodai (Ogdai) China; to Tuli, the nomad camps adjoining the share of Okkodai. Over these princes was to be exalted the great khan, chosen in a solemn assembly of all the princes. In 1228 Okkodai was proclaimed great khan. [Sidenote: [1237-1241 A.D.]] At first the question of succession, then the final consolidation of the empire in northern China, and then again the commencement of the war with the south kept the princes around the great khan, and it was only in 1235 that Okkodai sent his nephew Batu, son of Juji, together with Manku, son of Tuli, and his own son Kuiuk, to conquer the western lands; to their number was added Sabutai, famous for his Kiptchak campaign. First of all they conquered the Bulgarians on the Volga, and then came to the land of Riazan. Here they exacted from the princes a tribute of a tenth of all their possessions both in lands and in men; the courageous resistance of the Riazan princes proved unsuccessful, chiefly because the princes of northern Russia did not unite, but decided on defending themselves separately. After the devastation of Riazan and the slaughter of her princes (1237), followed that of Suzdal. Having taken Moscow, the Tatars marched to Vladimir, where they slew the family of the grand prince, while he himself was defeated and killed on the banks of the Sit (1238). Thence they were apparently going to Novgorod, but returned--probably to avoid the marshes. On their way back, Kozelsk detained them for a long time, but it was finally taken and pillaged.