After Genghis Khan's victory over the Naimans in 1204, the Naiman prince Kuchlug sought refuge with the Qara Khitai. Welcomed by Gurkhan Yelü Zhilugu, Kuchlug eventually seized power through a coup, ruling indirectly until Zhilugu's death in 1213, then taking direct control. Initially a Nestorian Christian, Kuchlug converted to Buddhism upon his rise among the Qara Khitai and initiated religious persecutions against the Muslim majority, which led to widespread discontent.

In 1218, to counter Kuchlug's growing threat, Genghis Khan dispatched General Jebe with 20,000 troops, including Genghis Khan's son-in-law, the Uyghur Barchuk, and possibly Arslan Khan, to confront Kuchlug, while Subutai led another force against the Merkits. The Mongol forces advanced through the mountains to Almaliq, with Subutai splitting off to target the Merkits. Jebe then moved to attack the Qara Khitai, defeating a large army at Balasagun and causing Kuchlug to flee to Kashgar. Jebe's announcement ending religious persecution won him local support, leading to a revolt against Kuchlug in Kashgar. Kuchlug fled but was captured by hunters and executed by the Mongols.

The Mongol victory over Kuchlug solidified their control over the Qara Khitai territory, extending their influence in Central Asia and setting the stage for further conflicts with the neighboring Khwarazm Empire.