Kuchlug in the context of "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. After his force of over 30,000 was defeated by Jebe at the Khitan capital Balasagun, Kuchlug faced rebellions over his unpopular rule, forcing him to flee to modern Afghanistan, where he was captured by hunters in 1218. The hunters turned Kuchlug over to the Mongols who beheaded him. Upon defeating the Qara Khitai, the Mongols now had a direct border with the Khwarazmian Empire, which they would soon invade in 1219.

The Irghiz River skirmish was a minor engagement fought between forces of the Khwarazmian Empire and the Mongol Empire during the early 13th century. While the occurrence of the skirmish itself is well-attested, its precise dating is uncertain, since the major chroniclers of the period give differing accounts. Modern historians have proposed two possible dates: 1209 or 1219. The background events are similar for each possible date: Genghis Khan, khagan of the Mongols, sent an army under his general Subutai to attack hostile forces (either a Merkit confederation or the renegade Naiman prince Kuchlug) in the former lands of the Qara-Khitai dynasty. Shah Muhammad, the ruler of the Khwarazmian Empire, received news of large armies operating along his northern borders and set out to confront them.

The Mongol army, which possibly also included the general Jebe and Genghis' eldest son Jochi, was surprised by the Shah very soon after defeating their initial target; Muhammad rejected peace overtures and initiated battle. The fierce engagement, between two armies of approximately equal strength, lasted until nightfall, but the Mongols probably had the upper hand. However, since they had been instructed to avoid any possible fighting, they abandoned their camp in secret during the night. The prowess of the Mongol soldiers displayed during the skirmish has been cited as a major reason for the Shah choosing a defensive strategy during the open warfare of 1220–21, for which this was a preliminary encounter.