Emperor Taizong of Tang
In 627 he attempted to levy horses from the vassal Tiele tribes after all his livestock died from a snowstorm. The Tiele revolted under a Xueyantuo coalition. Emperor Taizong of Tang wasted no time in allying with these Tiele and the Khitans in a joint attack. Illig was already facing internal dissent from the Göktürk generals jealous of the influence of Illig's Sogdian vizers.