The Battle of the Kalka River (1223) should have served warning to Kievan Rus of the existential threat posed by the Mongols, but instead the competing principalities remained divided. In 1237, a much larger Mongol army, under the command of Batu Khan, returned to administer the coup de grâce. Batu first subdued the kingdom of Volga Bulgaria, and their tribal allies, the Cumans and Alans. He then invaded Vladimir-Suzdal, razing Ryazan and the capital, Suzdal, while Grand Prince Vladimir II fled before his advance. Vladimir II was finally cornered at the Battle of the Sit River (1238); he was killed, his forces annihilated, and concerted resistance to the Mongols ended. Batu then split his forces, roaming south as far as the Crimea, subduing the principalities in turn. Unexpectedly leaving Novgorod untouched, the Mongol armies then advanced into eastern Europe, before the death of the Great Khan suspended operations.
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