Mongol invasion of Kievan Rus'

The Mongol Empire invaded and conquered much of the Kievan Rus' in the mid-13th century, sacking numerous cities such as Ryazan, Yaroslavl, Pereyaslavl and Vladimir, including the largest: Kiev (50,000 inhabitants) and Chernigov (30,000 inhabitants). The siege of Kiev in 1240 by the Mongols is generally held to mark the end of the state of Kievan Rus', which had already been undergoing fragmentation. Many other principalities and urban centres in the northwest and southwest escaped complete destruction or suffered little to no damage from the Mongol invasion, including Galicia–Volhynia, Pskov, Smolensk, Polotsk, Vitebsk, and probably Rostov and Uglich.

The Mongol campaign was heralded by the Battle of the Kalka River on 31 May 1223, which resulted in a Mongol victory over the forces of several principalities as well as the remnants of the Cumans under Köten. The Mongols retreated, having gathered their intelligence, which was the purpose of the reconnaissance-in-force. A full-scale invasion by Batu Khan followed, with most of Kievan Rus' overrun in 1236–1238. The Mongols captured Kiev in 1240 and moved west into Hungary and Poland. The heavy losses suffered by the Mongols during the invasion period significantly weakened subsequent campaigns, preventing the ruin of the Holy Roman Empire and more western countries.

The invasion was ended by the Mongol succession process upon the death of Ögedei Khan. Even those principalities who avoided physical conquest were eventually forced to accept Mongol supremacy in the form of tribute – as in the case of Galicia–Volhynia, Polotsk and Novgorod – if not outright vassalage, of the Golden Horde, until well into the 14th century.