The establishment of the Tang dynasty marked the comeback of Chinese expansionism, where it was also considered as the height of China as an ancient superpower. Under the Tang dynasty, China managed to maintain control over northern Vietnam, and returned to Korea. The Chinese Empire also managed to extend its control over Xinjiang and Central Asia, reaching as far west as the Aral Sea and Caspian Sea, although its rule over frontier regions was not consolidated, as China sought to gain loyalty from the Turkic and Sogdian tribes. At least, for once, the Chinese Empire managed to enroach into the Tibetan territory and occupied Lhasa, until they had to abandon due to difficult climate.