Kulun Beg succeeded Özmiş Khagan who was beheaded by the Ashina Shi.
When he was enthroned the Central Asian steppes were already conquered by the coalition of Uighur - Basmyl and Karluk.
Chinese emperor Xuanzong decided to destroy the last traces of Turkic khaganate and he sent general Wang Zhongsi (王忠嗣) over Kulun Beg’s forces.
Wang Zhongsi (王忠嗣) defeated the eastern flank of Turkic army headed by Apa Tarkhan.
However, a group including Po Beg, Bilge Khagan’s widow who was also Tonyukuk’s daughter, took refuge in China.