another golden age. Under the Tang dynasty, China managed to maintain control over northern Vietnam and 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. China also gained loyalty from the Turkic and Sogdian tribes at the northern and western borders. The Tang managed to encroach into the Tibetan territory and occupy Lhasa, until they had to abandon due to difficult climate. The Tang Chinese expansion was checked following the Battle of Talas in modern-day Kyrgyzstan, when the Tang was defeated by the Arabs. However, China remained strong enough to process a significant weight until the An Lushan Rebellion which crippled the Tang. The rebellion partly led to the collapse and implosion of the Tang into several warring states and kingdoms. After the Tang collapse, China would be divided into several smaller nations until the unification during the Yuan dynasty and Mongol empire. Fragmentation during Song, Jin, Liao dynasties When the Tang dynasty collapsed, China entered the Five Dynasties and Ten Kingdoms period. After this period, China remained fragmented and was divided into a number of smaller countries that emerged from the turmoil. These included the Song dynasty to the south and the Liao and Jin dynasties to the north. The Song, Liao, and Jin would continue to fight each other for centuries. As a result of perpetual instability, the Vietnamese eventually seceded from the union in the Battle of Bạch Đằng in 938, Song dynasty, unified much of China's south and launched an invasion of northern Vietnam in the process, but was repelled by Lê Hoàn. From then, the Song dynasty had struggled to reconsolidate back the borderland and inner territories, as well as repeated wars with Vietnam, the Liao dynasty, the Jin dynasty and the Western Xia. This had prevented the Song dynasty from ever taking any serious military expeditions. These various kingdoms (Song, Liao, Jin, Xia) would fight each other until they were all conquered and unified by the Yuan dynasty in 1279. Yuan dynasty The Yuan dynasty was founded by the Mongols in the traditional Chinese style in 1271. The Yuan dynasty and Mongol empire was characterized by unprecedented territorial expansionism north and west, reaching as far as Europe and West Asia. Yuan China undertook attempts to conquer other territories further east and south too. The Yuan dynasty launched