Yelü Dashi
The Qara Khitai empire was established by Yelü Dashi, who led nomadic Khitans west by way of Mongolia after the collapse of the Liao dynasty. The Jurchens, once vassals of the Khitans, had allied with the Song dynasty and overthrown the Liao. Yelü recruited Khitans and other tribes to form an army, and in 1134 captured Balasagun from the Kara-Khanid Khanate, which marks the start of the Qara Khitai empire in Central Asia. The Khitan forces were soon joined by 10,000 Khitans, who had been subjects of the Kara-Khanid Khanate. The Khitans then conquered Kashgar, Khotan, and Beshbalik. The Khitans defeated the Western Kara-Khanid Khanate at Khujand in 1137, eventually leading to their control over the Fergana Valley. They won the Battle of Qatwan against the Western Kara-Khanids and the Seljuk Empire on September 9, 1141, which allowed the Khitans to gain control over Transoxiana.