Emperor Taizong (r. 626–649) of Tang dynasty China, after subjugating the Eastern Turkic Khaganate, began to exert his military power toward the oasis city-states of the Tarim Basin, which were loosely allied with the Western Turkic Khaganate. In 640, Emperor Taizong sent the military commander Hou Junji to defeat and annex Gaochang—the first attempt by any Chinese dynasty to set up a permanent military and political presence in the region since Fu Jian in the 4th century. In 644, after Yanqi (Karasahr)—an ally in the campaign against Gaochang—turned against Tang and allied with the Western Turkic Khaganate, the Tang commandant at Gaochang, Guo Xiaoke, attacked and captured the Yanqi king Long Tuqizhi, but Yanqi subsequently rebelled. In 648, the ethnically Turkic Tang general Ashina She'e