Silla Unification of Korea (668): The Three Kingdoms End

The Silla unification of Korea was the process by which the south-eastern kingdom of Silla, allied with Tang China, conquered its rivals Baekje in 660 and Goguryeo in 668, ending the Three Kingdoms period. Silla then turned on its Tang allies and, by 676, had driven Chinese forces out of most of the peninsula. The resulting state, known as Unified Silla, ruled for more than two and a half centuries and laid foundations for a shared Korean identity.

Background: three rival kingdoms

For several centuries the Korean peninsula and southern Manchuria were divided between three kingdoms. Goguryeo, the largest, held the north and much of Manchuria, a power whose expansion is recorded on the Gwanggaeto Stele. Baekje ruled the fertile south-west, and Silla the south-east, centred on its capital at Gyeongju.

Silla was at first the smallest and most isolated, but in the 6th century it grew stronger. It adopted Buddhism, absorbed the Gaya confederacy and seized the Han River valley around modern Seoul in the 550s, which gave it a coast facing China. This made it a target for both its neighbours. In 642 Baekje captured some forty Silla fortresses, including the key stronghold of Daeya.

Goguryeo had meanwhile survived massive invasions by the Sui dynasty and by Tang Emperor Taizong in 645. Its powerful military dictator Yeon Gaesomun had seized control in 642 and refused to submit to China.

The Tang alliance

Desperate for help, Silla sent the nobleman Kim Chunchu to the Tang court in 648. Emperor Taizong agreed to an alliance against Baekje and Goguryeo. Silla adopted Tang court dress and the Tang calendar, signs of its new partnership. In 654 Kim Chunchu took the throne as King Muyeol, the first Silla king from the “true bone” rank rather than the highest “sacred bone” aristocracy.

The fall of Baekje (660)

In 660 a Tang army of about 130,000 men under Su Dingfang sailed across the Yellow Sea while Silla’s army, led by the general Kim Yu-sin, marched west. At Hwangsanbeol the Baekje general Gyebaek, with a small force often given as 5,000 men, held off the far larger Silla army in several clashes before being killed. The Baekje capital Sabi fell soon after, and King Uija surrendered.

A Baekje restoration movement, backed by Yamato Japan, fought on until 663. It was ended by the Tang naval victory at the Battle of Baekgang and the fall of the rebels’ fortresses.

The fall of Goguryeo (668)

Goguryeo held out for several more years. Its turning point came after the death of Yeon Gaesomun, usually dated to 665 or 666. His sons quarrelled, and the eldest, Yeon Namsaeng, fled to the Tang and offered to guide its armies.

Tang forces under the veteran general Li Ji advanced from the north-west, while Silla, now ruled by Muyeol’s son King Munmu, attacked from the south. In the ninth month of 668 the capital, Pyongyang, fell after a long siege, and King Bojang surrendered. Tang deported tens of thousands of Goguryeo families to China and set up the Protectorate General to Pacify the East at Pyongyang to govern the conquered lands.

The Silla-Tang War (670-676)

The Tang had intended to rule the whole peninsula, including Silla, through its own administrators. It had already named King Munmu a Tang governor and placed the former Baekje lands under Chinese commanderies. Silla refused to accept this.

From 670 Silla supported Goguryeo resistance fighters and seized former Baekje territory. One Goguryeo restoration leader, Geom Mojam, proclaimed a member of the old royal family, Anseung, as king; when the movement split and Geom Mojam was killed, Anseung fled south to Silla. King Munmu settled him and his followers at Geummajeo, in modern Iksan, as a client “King of Goguryeo”, later restyled King of Bodeok, a useful symbol of Silla’s claim to speak for the defeated kingdom. Tang sent large armies in response, and the war lasted six years. Korean sources record major Silla victories at Maeso fortress, near the Imjin River, in 675 and in a naval battle at Gibeolpo, at the mouth of the Geum River, in 676; Chinese sources give a different picture of some battles. Tang was also under growing pressure from the Tibetan Empire in the west.

In 676 the Tang moved its protectorate out of Pyongyang to Liaodong, in effect giving up its claim to rule the peninsula directly. Silla now controlled the land south of roughly the Taedong River and Wonsan Bay. Tang formally recognised this border in 735.

Key people

King Muyeol (Kim Chunchu, r. 654-661) built the Tang alliance and led the conquest of Baekje. King Munmu (r. 661-681), his son, completed the conquest of Goguryeo and won the war against Tang. Kim Yu-sin (595-673), Silla’s leading general and Muyeol’s brother-in-law, commanded its armies in the 660s. Emperor Gaozong of Tang (r. 649-683) oversaw the Chinese campaigns. Yeon Gaesomun (died c. 665-666) was Goguryeo’s dictator, whose death left the kingdom divided.

Consequences and legacy

Unified Silla greatly expanded its territory and population. It divided the land into nine provinces and five secondary capitals, granted officials office land and for a time replaced the nobles’ stipend villages with grain salaries, and drew Baekje and Goguryeo elites into its service, though at lower ranks than the Silla aristocracy. Its rigid bone-rank system, which tied office to birth, remained a source of tension.

The following century was a high point of Korean Buddhist art and learning, seen in the Bulguksa Temple and Seokguram Grotto at Gyeongju. Silla scholars and monks travelled widely in Tang China, and Gyeongju became a large, wealthy capital.

North of Silla, former Goguryeo general Dae Jo-yeong founded Balhae in 698 in Manchuria and the far north of Korea. Korean historians since the 18th century have called the era of Silla and Balhae the North-South States period, and debate how far the unification of 668 was a “true” unification. Unified Silla lasted until 935, when its last king surrendered to the new kingdom of Goryeo.

Most of what we know about these events comes from two Korean works written centuries later: the Samguk Sagi, an official history compiled by Kim Busik in 1145, and the Samguk Yusa, a collection of histories and legends assembled by the monk Iryeon in the 1280s. Both drew on older records now lost, and both tend to view the period from Silla’s side. Chinese histories of the Tang add a different perspective, especially on the war of 670-676, and historians compare the two traditions carefully.

King Munmu died in 681. According to the Samguk Sagi, he asked to be cremated and his ashes placed in the Eastern Sea, so that he might become a dragon and guard the kingdom against Japanese raiders. The islet of Daewangam off the Gyeongju coast is traditionally identified as his tomb.

Timeline

• 642: Baekje seizes forty Silla fortresses; Yeon Gaesomun takes power in Goguryeo.
• 648: Kim Chunchu concludes the alliance with Tang Emperor Taizong.
• 654: Kim Chunchu becomes King Muyeol.
• 660: Tang and Silla conquer Baekje; King Uija surrenders.
• 663: The Battle of Baekgang ends hopes of a Baekje restoration.
• 668, 9th month: Pyongyang falls; Goguryeo’s King Bojang surrenders.
• 670: War breaks out between Silla and Tang.
• 675-676: Silla victories at Maeso fortress and Gibeolpo.
• 676: Tang withdraws its protectorate to Liaodong.
• 681: King Munmu dies and, by tradition, is buried at sea.

Why it matters

Silla’s unification brought most of the Korean peninsula under one government for the first time. Unified Silla’s language, Buddhism and institutions became a common inheritance for later Korean states, from Goryeo to Joseon. The war against Tang also showed that a smaller kingdom could keep its independence beside the great Chinese empire, setting a pattern for Korea’s relations with China for centuries.