Silla's wars of unification (660–676)

In the seventh century three Korean kingdoms — Goguryeo, Baekje and Silla — competed for control of the peninsula, while Goguryeo also fought repeated wars with the Sui and Tang empires of China. In 648 Silla made a military alliance with Tang. Together they conquered Baekje in 660 and Goguryeo in 668.

The victory did not bring peace. Tang placed the conquered lands under its own military governments and treated Silla itself as a Tang prefecture. Between 670 and 676 Silla, joined by many refugees from the fallen kingdoms, fought Tang until the empire moved its headquarters out of Pyongyang. Silla then ruled the peninsula south of the Taedong River.

In South Korean schoolbooks these sixteen years are the story of how Silla “unified the Three Kingdoms”. That phrase is itself part of the history: it was a Silla claim, it leaves out most of Goguryeo’s old land in Manchuria, and North Korean and Chinese historians frame the same events differently. This page describes the wars and then explains those different views.

By the mid-600s Silla was in danger. In 642 Baekje captured Daeyaseong, a key fortress in today’s Hapcheon, and dozens of other Silla towns. Silla asked Goguryeo and Yamato Japan for help and was refused. The Silla noble Kim Chunchu then went to the Tang court, and in 648 he reached an agreement with Emperor Taizong.

According to King Munmu’s later letter to a Tang general, preserved in the Samguk sagi, Taizong promised that once Baekje and Goguryeo were defeated, Baekje and the land south of Pyongyang would go to Silla. The Encyclopedia of Korean Culture summarises the deal as a division along the Taedong River. Whether Tang ever meant to keep that promise became the central question of the war’s last phase.

Tang had its own reasons. Goguryeo had defeated the Sui dynasty’s huge invasions and had also held off Taizong’s campaign of 645. Conquering Baekje first would give Tang a base in the south and let it attack Goguryeo from two sides.

In the summer of 660 Tang sent an army that the Samguk sagi numbers at 130,000 men under Su Dingfang. The fleet met Silla’s crown prince, Kim Beommin, at Deokmul Island (today’s Deokjeokdo) and sailed to the mouth of the Geum River. Meanwhile Kim Yu-sin led about 50,000 Silla soldiers over the mountains from the east.

The Baekje general Gyebaek met the Silla army at Hwangsanbeol, near today’s Nonsan, with 5,000 men. Later tradition says he killed his own family before the battle so that they would not be enslaved. His troops won the first four clashes. The Samguk sagi then tells how the teenage hwarang Gwanchang charged the enemy twice and was beheaded; his death roused the Silla army, which overran the Baekje lines. Gyebaek died on the field.

On the same day the Tang army defeated Baekje troops at Gibeolpo on the Geum estuary. The allies surrounded the capital, Sabi (today’s Buyeo). King Uija fled to Ungjin (Gongju), but within days he surrendered. Su Dingfang took the king, members of the royal family and officials, and about 12,000 people to China. Tang divided Baekje into five military commanderies, centred on Ungjin, instead of handing it to Silla.

Baekje’s sudden collapse left its provinces and armies largely intact. Within weeks, Heukchi Sangji gathered tens of thousands of men at Imjonseong in today’s Yesan, while the royal kinsman Boksin and the monk Dochim based themselves at Juryuseong. The Encyclopedia of Korean Culture says they recovered some 200 fortresses and repeatedly besieged the Tang garrison left at Sabi.

The loyalists asked Yamato Japan to send back Prince Buyeo Pung, a son of King Uija who had lived at the Yamato court. Empress Saimei moved her court to Asakura in northern Kyushu in 661 to prepare an expedition and died there; her successor, the future Emperor Tenji, continued the effort. In 662 a Yamato fleet of 170 ships brought Pung home as king, and in 663 a much larger army followed.

The movement was weakened by quarrels. Boksin killed Dochim, and in 663 Pung had Boksin executed on suspicion of plotting against him. Tang and Silla then closed in on Juryu. In the eighth lunar month of 663, at the mouth of the Baek River (Baekgang, called Hakusukinoe in Japan), a Tang fleet of 170 ships fought the Yamato fleet for two days. According to the Nihon Shoki the Yamato commanders attacked without a plan, were enveloped from both sides and lost many ships and men. Juryu surrendered, Pung fled to Goguryeo, and many Baekje nobles sailed to Japan with the retreating fleet.

Tang now tried a different approach. It appointed Uija’s son Buyeo Yung as governor of Ungjin and in 664 and 665 made Silla swear formal peace oaths with him, the second on Chwirisan hill in Gongju. For Silla, which had carried much of the fighting and had fed the Tang garrison for years, this was a bitter result.

Tang’s first attack on Goguryeo after Baekje’s fall began in 661. Su Dingfang besieged Pyongyang for months, while Goguryeo’s dictator Yeon Gaesomun destroyed another Tang army on the Sasu River. Early in 662 Kim Yu-sin led a Silla convoy of some two thousand carts of grain north through snow and ice to feed the Tang besiegers; many men and animals froze to death. Soon afterwards the Tang army gave up and withdrew.

What Tang could not do by force was made possible by Goguryeo’s own divisions. After Yeon Gaesomun died, his sons quarrelled. The eldest, Yeon Namsaeng, was driven out by his brothers and went over to Tang, and his uncle Yeon Jeongto surrendered twelve fortresses to Silla. In 667 a Tang army under Li Ji, guided by Namsaeng, took the key fortress of Xincheng (in today’s Fushun) and swept through the forts north of the Yalu.

In 668 the Tang armies converged on Pyongyang while Silla attacked from the south. After a siege of more than a month King Bojang surrendered; the monk Sinseong opened the gates to end the resistance of Yeon Namgeon. Tang took the king and, according to the Samguk sagi, more than 200,000 people to China, and set up the Protectorate General to Pacify the East at Pyongyang to rule Goguryeo’s former lands.

Silla prepared for war with its former ally throughout 669 and struck first. In the spring of 670 ten thousand Silla troops under Seol Oyu and ten thousand Goguryeo loyalists under Go Yeonmu crossed the Yalu and fought Tang and Mohe forces near Ogolseong in Liaodong. At the same time the Goguryeo noble Geom Mojam raised a rebellion and proclaimed Anseung, a member of the Goguryeo royal family, king at Hanseong (today’s Chaeryong). Silla recognised Anseung as King of Goguryeo and later settled his court at Geummajeo, in today’s Iksan.

From the summer of 670 Silla also attacked the Tang-held commandery of Ungjin, capturing more than eighty Baekje towns. In 671 it defeated a Tang relief army at Seokseong and organised the old Baekje capital as its own province of Soburi. Tang answered from the north: the armies of Gao Kan and Li Jinxing crushed the Goguryeo rebels, occupied Pyongyang in 672, inflicted a heavy defeat on Silla at Seokmun and in 673 destroyed the Goguryeo loyalists on the Horo River, a stretch of the Imjin. Silla switched to defence, built fortresses and posted a fleet in the Yellow Sea. In 674 Emperor Gaozong stripped King Munmu of his titles and proclaimed Munmu’s brother Kim Inmun king of Silla.

The decisive year was 675. Liu Rengui defeated Silla at Chiljungseong early in the year, and Munmu sent envoys to apologise while continuing to fight. In the ninth lunar month Xue Rengui’s fleet was driven off at Cheonseong near the Han River mouth, and on the 29th the Tang army camped at Maesoseong, which the Samguk sagi numbers at 200,000 men, was routed or withdrew, leaving 30,380 horses. The Samguk sagi lists eighteen further Silla victories that year.

In 676 Tang, now facing attacks by the Tibetan empire on its western frontier, wound down the war. In the eleventh lunar month a Silla fleet under Sideuk lost its first clash with Xue Rengui at Gibeolpo on the Geum estuary but went on to win twenty-two engagements. Tang moved the seat of its protectorate from Pyongyang to Liaodong (today’s Liaoyang) and in 677 to Xincheng. Silla kept the land south of the Taedong River; Tang formally recognised this border only in 736.

The sources speak mainly of kings and generals, but they also show what the wars meant for ordinary people. King Munmu’s letter of 671 describes Silla farmers conscripted year after year, grain hauled both north to Pyongyang and west to the Tang garrison at Ungjin, oxen and horses worked to death, and harvests lost, so that Silla people ate grass roots while the Tang garrison had food to spare.

Conquest meant mass removal. Su Dingfang carried off the Baekje king with about 12,000 people in 660. After Pyongyang fell in 668 more than 200,000 people were taken to Tang, and in 669, according to the Samguk sagi, Tang moved 28,300 Goguryeo households to thinly settled regions south of the Yangtze and Huai rivers and in the west.

Others fled east. After Baekgang many Baekje nobles and commoners settled in Japan, where the Nihon Shoki records them receiving court ranks, land and rations; Baekje officers designed the mountain forts that Yamato built against a feared invasion. Goguryeo refugees poured into Silla, where Anseung’s small Bodeok kingdom survived until 684, and Silla later enrolled Goguryeo, Baekje and Mohe people in separate units of its royal army.

For Silla the wars produced a much larger state. Its kings began to speak of having united the “Three Han” (samhan iltong), gave court ranks to former Baekje and Goguryeo nobles, and reorganised the country into nine provinces with a royal army of nine banners. Relations with Tang were frozen for decades and restored only in the early eighth century.

That power was Balhae, founded in 698 in the former Goguryeo lands of Manchuria by Dae Joyeong, who led Goguryeo and Mohe people. For about two centuries Silla in the south and Balhae in the north existed side by side, the era that many Korean historians now call the North–South States period.

For Tang, the conquests were only partly successful. It destroyed two kingdoms but could not hold the peninsula, and the Encyclopedia of Korean Culture notes that the costs of the long campaign in the east were felt in the Tang provinces that supplied soldiers. For Yamato Japan, the defeat at Baekgang set off a building programme of guard posts and beacons, the Mizuki dyke and Korean-style mountain forts built under Baekje officers; in 670 the Samguk sagi records that Wa had changed its name to “Nihon”.

In South Korea the traditional name is “Silla’s unification of the Three Kingdoms”, and Kim Yu-sin and King Munmu are celebrated figures. Supporters of this view stress that Silla ended centuries of war, absorbed Goguryeo and Baekje people and culture, and laid the basis for the later single Korean states of Goryeo and Joseon. Critics, including many South Korean scholars, point out that Silla invited a foreign empire to destroy fellow kingdoms, that it won only the land south of the Taedong River, and that most of Goguryeo’s territory went first to Tang and then to Balhae. For this reason many historians now also speak of a North–South States period, in which Silla and Balhae coexisted, rather than only of “Unified Silla”.

North Korean historians reject the idea that Silla unified the nation. In their account Goryeo, founded in 918 and claiming Goguryeo’s heritage, was the first state to unite the Korean people, and they call the post-668 period “Late Silla”.

Traditional Chinese histories record these events as campaigns of the Tang court and, as the case of Maesoseong shows, can pass over Tang defeats that the Korean chronicle emphasises. In modern China the Northeast Project, a state-backed research programme that ran from 2002 to 2007, argued that Goguryeo was a local regime of ancient China rather than a Korean kingdom, a position sharply criticised by Korean and other historians. In Japan the wars are remembered chiefly through the defeat at Hakusukinoe and the arrival of Baekje refugees, who received ranks and land at the Yamato court.

These disagreements matter because each modern state reads its own origins into the seventh century. A careful account keeps the medieval claim of samhan iltong, the modern nation-state debates and the experience of the people who lived through the wars as three different things.

The main Korean narrative is the Samguk sagi, compiled in 1145 under Kim Busik, almost five centuries after the events. For these years it draws on lost Silla records, which give day-by-day detail for Silla’s own campaigns, and on Chinese histories such as the Old and New Books of Tang and the Zizhi Tongjian. For Baekje and Goguryeo in these years it relies heavily on Chinese material, so the defeated kingdoms speak mostly through their enemies. It also preserves long documents, notably Xue Rengui’s letter of 671 accusing Silla of treachery and King Munmu’s detailed reply, which is the fullest statement of Silla’s grievances.

The Nihon Shoki (720) is the key source for Yamato’s intervention and gives the Baekgang battle day by day using the sexagenary day cycle. It sometimes disagrees with the Korean record: it places Yeon Gaesomun’s death in 664, while the Samguk sagi places it in 666. Tomb epitaphs of Baekje and Goguryeo émigrés excavated in China add another voice, sometimes giving family histories and careers that the chronicles omit.

Dates in these sources follow the Chinese-style lunisolar calendar used by Silla and Tang, so a date such as “the 29th day of the 9th month” of 675 does not correspond to a modern September. Converted with standard calendar tables, the Hwangsanbeol battle falls on 20 August 660 and Baekgang on 4–5 October 663 in the Julian calendar. Numbers of troops are another difficulty: figures such as 130,000 Tang soldiers in 660 or 200,000 at Maesoseong are widely regarded as inflated or as totals for whole theatres.

Why did Silla and Tang go to war? The traditional explanation is territorial: Tang broke Taizong’s promise and tried to rule the whole peninsula through the Ungjin commandery, the Protectorate at Pyongyang and the designation of Silla as the “Gyerim Great Area Command”. The Encyclopedia of Korean Culture article by Lee Sang-hoon adds a more immediate cause: Tang’s repeated interference in Silla’s military command during the joint campaigns, which angered the Silla leadership, together with a dispute over the strategic town of Biyeolhol. He characterises the conflict as a preventive war launched by Silla to seize key positions before Tang could move against it.

How decisive was Maesoseong? The Samguk sagi presents it as a crushing victory, while the Zizhi Tongjian does not mention a battle there at all. Kim Byeong-hee has argued that the phrase in the Samguk sagi can be read as Silla attacking a Tang army that was already retreating for lack of supplies, that the captured horses could not have fitted in the small mountain fort, and that the Tang commander Li Jinxing was not punished but redeployed. Others treat Maesoseong as one part of a wider 675 campaign that included Cheonseong, Chiljungseong and other forts, in which Silla’s successful defence of the Imjin line was what counted.

Why did Tang withdraw? Scholars weigh Silla’s military resistance against Tang’s overstretch: the Tibetan offensives of 676 forced Tang to shift its armies west, supply lines across the sea were fragile, and the eastern provinces were exhausted. Places are disputed too. The Encyclopedia of Korean Culture gives two candidate sites for Maesoseong, the Daejeon-ri fortress in Yeoncheon and Daemosanseong in Yangju, and the locations of the restoration capital Juryuseong and of the Baekgang battlefield — on the lower Geum River or further south in today’s North Jeolla — have been argued over since the eighteenth century.