I think someone tore the relevant pages out your Little Red Book of Tibetan History.:
During the reign of King Songtsen Gampo (629-49) Tibet became a great military power and her armies marched across Central Asia. He promoted Buddhism in Tibet and sent one of his ministers and other young Tibetans to India for study. He first took a Tibetan princess from the Shangshung King as his wife and then obtained a Nepalese consort. After invading the Chinese Empire he also obtained a Chinese princess as one of his wives. The two latter wives have been given prominence in the religious history of Tibet because of their services to Buddhism.
During the reign of King Trisong Detsen (755-97) the Tibetan Empire was at its peak and its armies invaded China and several Central Asian countries. In 763 the Tibetans seized the then Chinese capital at Ch'ang-an (present day Xian). As the Chinese Emperor had fled, the Tibetans appointed a new Emperor. This memorable victory has been preserved for posterity in the Zhol Doring (stone pillar) in Lhasa :
In fact it seems that Tibet in fact owned a fair whack of China.............Give it Back!!
