Silla’s war with Tang (676) and the rise of Balhae

The seven-year war between Silla and Tang ended at Gibeolpo in 676, eight years after Goguryeo fell.

When Baekje and Goguryeo fell, the alliance that had defeated them fell apart. Tang wanted the whole peninsula under its own control and began to interfere with Silla’s command of its own troops. Silla’s leaders refused. The war that followed decided that Silla, not Tang, would rule the south of the peninsula. Meanwhile, in the old Goguryeo lands in the north, a new state named Balhae arose in 698. Korean historians often call the time when Silla in the south and Balhae in the north stood side by side the age of the Northern and Southern States.

Silla against Tang, 670 to 676

The Encyclopedia of Korean Culture describes the war as lasting seven years. It began in the third month of 670, when Silla struck first at Ogol-seong, north of the Amnok River. In the same period groups of Goguryeo people rose against Tang, and the Goguryeo revival movement went on from 670 to 684. Silla did not always win: in the eighth month of 672 it suffered a heavy defeat at Seokmun. The turning point came in the ninth month of 675, when Silla won the battle of Maeso-seong on land. In the eleventh month of 676 a sea battle at Gibeolpo, at the mouth of the Geum River, ended the war.

Victory let Silla bring together most of the former lands of Baekje and the southern part of Goguryeo under one government, which is why 676 is taught as the year of unification of the three kingdoms. Historians also point out its limits: much of Goguryeo’s former territory in the north and in Manchuria stayed outside Silla, and soon became the heart of Balhae.

Escape from Yingzhou

Balhae, 698 to 926

Dae Joyeong led his people further east, about 2,000 li from Yingzhou, and in 698 founded a state at Dongmo-san, today identified with the Chengshanzi mountain fortress near Dunhua in Jilin province. He first called it Jin-guk; the name Balhae was adopted in 713. The records describe Dae Joyeong as a "separate branch of Goguryeo", as a Songmal Malgal, and as a former Goguryeo general, and historians think all three descriptions together explain who he and his people were: Goguryeo refugees and Malgal groups who built one state.

Balhae moved its capital several times. The second king, Mu, moved to Hyeonju according to recent research, though older work placed that move in Mun’s reign; the third, Mun, moved to Sanggyeong, then late in his reign to Donggyeong; and the fifth king, Seong, moved back to Sanggyeong in 794, where the capital stayed until the end. The kingdom was organised into five capitals, fifteen prefectures and sixty-two districts, and it used era names of its own, such as Inan and Daeheung, to show it stood as an equal to its neighbours. In the early ninth century, under King Seon, it brought most Malgal groups under its rule and its borders reached Silla’s. Chinese writers called it Haedong seongguk, the flourishing land east of the sea.

Balhae’s end came quickly. The Khitan, united under Yelü Abaoji, founded the Liao state in 916, and quarrels within Balhae’s ruling class are often given as one reason it had grown weak, though the evidence is thin. In 926 a Khitan invasion destroyed it. Some of its people kept up resistance in the old Balhae lands, and many others moved south to Goryeo, the state that went on to reunite the peninsula in 936.