Background

Western Turkic Empire in present-day Turkestan was founded as the result of the partition of the main empire after the death of Tardu in 603. It was also called On Ok ("Ten arrows") referring to ten powerful tribes in the empire. Five tribes (so-called Dulo) to the northeast and five tribes to the southwest (so-called Nushibi) formed the two rival factions, the border line being Ili River.

Sibir as the monarch

In 630, Dulo clan of tribes together with Karluks revolted against Tong the most successful ruler of the empire who was supported by the rival Nushibi faction. Külüg Sibir murdered Tong who was his nephew and declared himself as the khagan (emperor) with the support of Dulo clan. According to S. G. Klyashtorny and T. I. Sultanov he was trying to end the tension between the khagan and the vassal tribes. However Nushibi faction didn't accept his title and supported Tong's son to throne. Although Külüg Sibir asked for Dulu support, next year he had to abdicate. He escaped to Altay Mountains where he was killed by Nushibi partisans.