The Invasion of Europe: Batu, Subutai, and the Limits of Expansion

The kurultai of 1235 decided to launch a great western campaign under the nominal command of Batu Khan, son of Jochi, with Subutai as the campaign's true chief military strategist. Mongol forces first subdued the Volga Bulgars and the Cuman-Kipchaks of the southern Russian steppes (1236-1237), and the systematic invasion of Kievan Rus began in the winter of 1237, exploiting frozen rivers as fast routes for cavalry advancing on fortified cities. Ryazan fell in December 1237, Vladimir in February 1238, and Kiev, the historic capital of the Rus, was besieged and destroyed in December 1240; Novgorod alone escaped conquest, apparently because the spring thaw turned the surrounding marshy terrain impassable for cavalry.