The foreign relations of Tibet are documented from the 7th century onward, when Buddhism was introduced by missionaries from India. The Tibetan Empire sparred with Tang China for control over territory, but relations became good with a peace marriage. Tibet was conquered by the Mongol Empire and that changed its internal system of government, introducing the Dalai Lamas, as well as subjecting Tibet to foreign hegemony under the Yuan Dynasty. Tibetan foreign relations during the Ming Dynasty are opaque, with Tibet being either a tributary state or under full Chinese sovereignty. But by the 18th century, the Qing Dynasty indisputably made Tibet a subject. In the early 20th century, after a successful invasion, Britain established a trading relationship with Tibet and was permitted limited di