Mongol invasion of Kievan Rus'

The Mongol Empire invaded and conquered Kievan Rus' in the mid-13th century, destroying numerous cities including the largest such as Kiev (50,000 inhabitants) and Chernigov (30,000 inhabitants). The Mongol siege and sack of Kiev in 1240 is generally held to mark the end of Kievan Rus'. Many other major Rus' principalities and urban centres in the northwest escaped destruction or suffered little to no damage from the Mongol invasion, including the Novgorod Republic, Pskov, Smolensk, Polotsk, Vitebsk, and probably Rostov and Uglich. The campaign was heralded by the Battle of the Kalka River in May 1223, which resulted in a Mongol victory over the forces of several Rus' 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 of Rus' by Batu Khan followed, from 1237 to 1241. The invasion was ended by the Mongol succession process upon the death of Ögedei Khan. Most Rus' principalities were forced to submit to Mongol rule and became vassals of the Golden Horde, excluding the Novgorod Republic and a few others. The invasion, facilitated by the beginning of the breakup of Kievan Rus' in the 13th century, had profound ramifications for the history of Eastern Europe, including the division of the East Slavic people into three distinct separate nations: modern-day Belarusians, Russians, and Ukrainians. The Mongols had plans to conquer Eastern Europe long before Batu's campaign in 1237. In 1207, Genghis Khan sent his eldest son Jochi to conquer the tribes north of the Selenga River and in the Irtysh valley, which included the lands of Eastern Europe in the Jochi Ulus. However, these plans were not implemented during the lifetime of Genghis Khan. In 1222-1224, Subedei and Jebe conducted a campaign with a 30,000-strong army in Transcaucasia and Southeastern Europe, which is traditionally considered reconnaissance.