Dae Joyeong Founds the Kingdom of Balhae

In the closing years of the seventh century, the northeast borderlands of East Asia experienced violent political realignments. Decades after the Tang dynasty allied with Silla to crush the ancient kingdom of Goguryeo, displaced populations settled under imperial surveillance around Yingzhou in modern Liaoning. In 696, a major uprising led by Khitan leaders shattered Tang control over the district. Amid the breakdown of imperial authority, diverse refugee populations moved eastward toward the Liao River valley, seeking safety and autonomy far from the reach of the Tang court under Wu Zetian.

Among these fleeing groups were remnants of Goguryeo communities alongside Mohe tribes. Imperial authorities attempted to pacify two prominent leaders, granting the titles of Duke of Zhen to Tae Chungsang and Duke of Xu to Kŏlsa Piu. When Kŏlsa Piu rejected the overture, Tang forces pursued and destroyed his followers, while Tae Chungsang died during the eastward flight. Leadership then fell to Chungsang's son, Tae Choyŏng (Dae Joyeong), who rallied both Goguryeo and Mohe survivors. At the Battle of Tianmenling, his combined force dealt a decisive defeat to the pursuing Tang general Li Kaigu, exploiting mountain terrain and severing imperial pursuit routes.