Mongol conquest of the Qara Khitai

The Mongol Empire conquered the Qara Khitai (Western Liao Empire) in the year 1218 AD. Prior to the invasion, war with the Khwarazmian Empire and the usurpation of power by the Naiman prince Kuchlug had weakened the Qara Khitai. When Kuchlug besieged Almaliq, a city belonging to the Karluks, vassals of the Mongol Empire, and killed their ruler Ozar, who was a grandson-in-law to Genghis Khan, Genghis Khan dispatched a force under command of Jebe and Barchuk to pursue Kuchlug.

Source: Wikipedia — Mongol conquest of the Qara Khitai (CC BY-SA 4.0)