당나라는 왜 한반도 정복에 실패하였는가?
Although they were formerly enemies, the Tang accepted officials and generals of Goguryeo into their administration and military, such as the brothers Yeon Namsaeng (634–679) and Yeon Namsan (639–701). From 668 to 676, the Tang Empire would control northern Korea. However, in 671 Silla broke the alliance and began the Silla–Tang War to expel the Tang forces. At the same time the Tang faced threats on its western border when a large Chinese army was defeated by the Tibetans on the Dafei River in 670. By 676, the Tang army was expelled out of Korea by Unified Silla. Following a revolt of the Eastern Turks in 679, the Tang abandoned its Korean campaigns.
expelled out of Korea by Unified Silla