Who invaded Kiev in the 1200s and forced Russians to flee to Moscow?

In the 1200s, Kiev was invaded by the Mongol Empire under the leadership of Batu Khan, a grandson of Genghis Khan. The Mongols launched a brutal campaign known as the Mongol invasion of Kievan Rus, which led to the sacking of Kiev in 1240. This invasion caused many Russians to flee to the northeastern regions, particularly to Moscow, which later became a center of resistance and power against Mongol rule.