Emperor Taizong of Tang (r. 626–649) of Tang Dynasty China, after subjugating the Eastern Turkic Khaganate, began to exert his military power toward the Western Regions, then dominated by the Western Turkic Khaganate as well as a number of city-states loosely allied with the Western Turkic Khaganate. In the year 640, Emperor Taizong sent the military commander Hou Junji to defeat and annex Gaochang—the first attempt by any Chinese dynasty to set up permanent military and political presence in the region since Fú Jiān in the 4th Century. In 644, after Yanqi—an ally in the campaign against Gaochang—turned against Tang and allied with Western Turkic Khaganate, Tang's commandant at Gaochang, Guo Xiaoke (郭孝恪), attacked and captured Yanqi's king Long Tuqizhi (龍突騎支), but Yanqi subsequently broke