Their daughters were also given husbands of tribes important to the expansion of the Mongol Empire and they were expected to aid their father by taking over power their while their husbands served him as his gurugen, or sons-in-law. The Uyghurs were enemies of the Western Liao and their chieftain requested a marriage alliance with Genghis Khan, hoping to become a 'fifth son' to him.
Western Liao
Genghis Khan