The invasions, a retaliation against a Goguryeo raid in 242, destroyed the Goguryeo capital of Hwando, sent its king fleeing, and broke the tributary relationships between Goguryeo and the other tribes of Korea that formed much of Goguryeo's economy. Although the king evaded capture and eventually settled in a new capital, Goguryeo was reduced to such insignificance that for half a century there was no mention of the state in Chinese historical texts.
By the time Goguryeo reappeared in Chinese annals, the state had evolved into a much more powerful political entity—thus the Wei invasion was identified by historians as a watershed moment in Goguryeo history that divided the different stages of Goguryeo's growth. In addition, the second campaign of the war included the furthest expedition into Manchuria by a Chinese army up to that time and was therefore instrumental in providing the earliest descriptions of the peoples who lived there.
The polity of Goguryeo developed among the peoples of Manchuria and the Korean Peninsula during the 1st and 2nd century BC as the Chinese Han dynasty extended its control to Northeast Asia, creating the Four Commanderies of Han. As it grew and centralized, Goguryeo increasingly contacted and conflicted with China. Gogeryeo consolidated its power by conquering the territories on the north of the peninsula which were under Chinese rule. When the power of the Han dynasty declined to internal turmoils in the 2nd century AD, the warlord Gongsun Du came to control the commanderies of Liaodong (遼東) and Xuantu, directly adjacent to Goguryeo. Gongsun Du's faction often quarreled with Goguryeo despite initial cooperation, and the conflict culminated in the Goguryeo succession feud of 204, which Gongsun Du's successor Gongsun Kang exploited. Though the candidate supported by Gongsun Kang was eventually defeated, the victor Sansang of Goguryeo was compelled to move his capital southeast to Hwando (present-day Ji'an, Jilin) on the Yalu River, which offered better protection. Gongsun Kang moved in and restored order to the Lelang Commandery and established the new Daifang Commandery by splitting the southern part of Lelang.
Compared to the agriculturally rich former capital Jolbon, Hwando was situated in a mountainous region with little arable land. To sustain the economy, Hwando had to constantly extract resources from the peoples in the countryside, which included the tribal communities of Okjeo and Ye. The Okjeo were said to have worked as virtual slaves to the Goguryeo king, hauling provisions (such as cloth, fish, salt and other sea products) from the peninsula's northeast to the Yalu basin, reflecting the arrangement that Goguryeo had to adopt after the entry of Gongsun Kang. By the 230s, Goguryeo had regathered their strength from these tributary relations and regained their presence in the Jolbon region. In 234, the Han dynasty's successor state Cao Wei established friendly contact with Goguryeo, and in 238 an alliance between Wei and Goguryeo destroyed their common enemy Gongsun Yuan, the last of the Gongsun warlords (See Sima Yi's Liaodong campaign). Wei took over all of Gongsun Yuan's territories, including Lelang and Daifang — now Wei's influence was extended into the Korean Peninsula, adjacent to Goguryeo.
The alliance broke down in 242, when King Dongcheon of Goguryeo plundered the Liaodong district of Xi'anping (西安平; near present-day Dandong, Liaoning) at the mouth of the Yalu River. The motive for the raid, though not exactly clear, was suggested to be either a search for new agricultural land or competition for the control of the "Small River Maek" (小水貊) people nearby, a branch of the Goguryeo people known for their excellent bows. In any case, since a Goguryeo presence there would cut off the land routes between the Chinese heartland and the peninsular commanderies, the Wei court reacted most strongly to this apparent threat to their control of Lelang and Daifang.
In response to Goguryeo's aggression, the Inspector of You Province (幽州刺史), Guanqiu Jian, set out from Xuantu Commandery into Goguryeo with seven legions — amounting to 10,000 infantry and cavalry in total — in 244. From the seat of government in Xuantu (near present-day Shenyang, Liaoning), Guanqiu Jian's army went up the valley of the Suzi River (蘇子河), a tributary of the Hunjiang River, to present-day Xinbin County, and from there crossed the watershed to the east and entered the Hunjiang River valley. King Dongcheon marched with 20,000 infantry and cavalry out from his capital Hwando to meet the advancing army. The king's army traveled through several river valleys and met Guanqiu Jian's army at the junction of the Fu'er River (富爾江) and the Hunjiang River, a place known as Liangkou (梁口; present-day Jiangkou village 江口村 in Tonghua). Liangkou was to become the site of the first battles between Guanqiu Jian and King Dongcheon.
Sources differ on how the battles played out. The later Korean source Samguk Sagi state that Guanqiu Jian's army invaded in the eighth lunar month of the year, but was twice defeated before winning the crucial battle that sent the king back to the capital. The first battle, according to Samguk Sagi, pitted King Dongcheon's 20,000 foot and horse soldiers against Guanqiu Jian's 10,000-man-strong army on the Hunjiang River, which Goguryeo won and beheaded 3,000 Wei soldiers. The second engagement was described to have happened in a "Dale of Liangmo" (梁貊之谷), where Goguryeo again bested and captured and killed 3,000 more soldiers. The two victories seemed to have got into the king's head as he remarked to his generals: "The Wei army, so enormous, cannot match a small force of ours, Guanqiu Jian is a great general of Wei, and today his life is in my hands!" He then led 5,000 ironclad horsemen to lead the charge against Guanqiu Jian, who put his troops in square formation and fought desperately. In the end, 18,000 Goguryeo men were killed in this last battle, and the defeated king fled to the Plain of Yalu (鴨綠原) with a little more than a thousand horsemen.
In contrast, the near-contemporary "Biography of Guanqiu Jian" in volume 28 of Records of Three Kingdoms, containing the Chinese account of this battle, state that King Dongcheon was repeatedly defeated in the tremendous fight at Liangkou and was forced to flee. Japanese researcher Hiroshi Ikeuchi points out that the Korean account was transformed from Guanqiu Jian's biography, reversing the results of the battles before Liangkou in order to save Goguryeo's "face". The same researcher also suggests that the aforementioned "Dale of Liangmo" place was fabricated by the biased historian sympathetic to Goguryeo. Nonetheless, both Chinese and Korean sources agree on the fact that King Dongcheon ultimately lost the battle of Liangkou and headed back to Hwando.
The Wei army gave chase to the routed Goguyeo army after the battle of Liangkou. According to the Chinese source History of Northern Dynasties, Guanqiu Jian reached Chengxian (赬峴), determined to be the present-day mountain pass Xiaobancha Ridge (小板岔嶺), also called Banshi Ridge (板石嶺). Since the mountainous region rendered the cavalry ineffective, the Wei army fastened the horses and chariots there and climbed up to mountain city of Hwando. Guanqiu Jian first struck the stronghold guarding the main city and then descended upon the capital, where the Wei army wrought much destruction, slaughtering and capturing over thousands of people. Guanqiu Jian specifically spared the tomb and family of Deukrae (得來), a Goguryeo minister who frequently remonstrated against aggression toward Wei and starved himself to death in protest when his advices went unheeded. The king and his family fled the capital.
With the Goguryeo capital subjugated, Guanqiu Jian returned to You Province with his army in around June 245. On the way back, he had a tablet erected in Chengxian commemorating his victory, explaining the course of events, and listing the generals who participated in the campaign. A fragment of the monument was discovered in 1905, near the end of the Qing dynasty, bearing the following mutilated inscription:
|In the 3rd year of Zhengshia the Goguryeo [?invaded]...||正始三年高句驪[?寇]|
|...commanded the seven legions, and attacked the Goguryeo. In the 5th [?year]b...||督七牙門討句驪五[?年]|
|...again the remaining enemies. In the 6th year, the 5th monthc, he led back [?his army]...||復遣寇六年五月旋[?師]|
|General Who Exterminates Invaders, Wuwan Chanyu of Weid...||討寇將軍魏烏丸單于|
|General Who Intimidates Invaders, Chief Village Marquis...||威寇將軍都亭侯|
|Expeditionary Major-General possessing...||行裨將軍領|
King Dongcheon had returned to the abandoned capital of Hwando after the Wei army retreated homeward, but in the same year Guanqiu Jian sent the Grand Administrator of Xuantu, Wang Qi (王頎), in pursuit of the king. Since the capital had been so ravaged and rendered defenseless by the previous campaign, the king had to flee again with his nobles of several ranks to South Okjeo (also known as Dongokjeo, "East Okjeo"). According to the Samguk Sagi, the king's escape was aided by Mil U (密友), a man of the Eastern Department (東部), when the king's troops had all but scattered to the last handful at Jukryeong Pass (竹嶺). Mil U said to the king, "I will go back and hold the enemy at bay while you make good your escape," and held the narrow pass with three or four soldiers while the king made his way to regroup with a band of friendly troops. The king offered a reward to anyone who could bring Mil U back to safety, and a Yu Ok-gu (劉屋句) found Mil U lying on the ground with grievous injuries. The king was so delighted to recover his faithful retainer that he personally nursed Mil U back to life.
The chase from Hwando to South Okjeo took the two parties across the Yalu River into North Korea. The precise route of the chase may have passed by present-day Kanggye, from where there are two possibilities: one heading east through the Rangrim Mountains then south to present-day Changjin; the other following the Changja River south then turning east to reach Changjin. From Changjin, the pursuer and the pursued followed the Changjin River (長津江) south until they reached the vast and fertile Hamhung plains, where the river flowed into the East Korea Bay. It was here in Hamhung that the South Okjeo people thrived, and thus King Dongcheon came here for refuge. When Wang Qi's army arrived, however, the Okjeo tribes were all defeated, with 3,000 tribesmen killed or captured. The king fled again, and the Wei army turned toward North Okjeo.
The Samguk Sagi relates to an event that purported to have happened in South Okjeo: Yu Yu (紐由), another man of the Eastern Department, feigned the surrender of King Dongcheon to stop the Wei pursuit. Bearing food and gifts, Yu Yu was allowed into the camp of an unnamed Wei general. When the general received him, Yu Yu pulled out a hidden dagger from under the plates and fatally stabbed the Wei general. He was likewise killed by the attendants at the next moment, but the damage had been done — the Wei army, having lost their commander, was thrown into confusion. King Dongcheon took this opportunity to gather his forces and struck his enemy in three columns. The Wei armies, unable to recover from the confusion, "at last retired from Lelang". This passage was not paralleled in Chinese records, and Hiroshi Ikeuchi points out its errors: the author of this passage in Samguk Sagi regarded the region of South Okjeo and Lelang as identical, while in fact they are on opposite sides of the peninsula; also, the references to the "Eastern Department" for Yu Yu and Mil U are anachronistic, since Goguryeo did not divide the country into departments until the middle of the Goguryeo dynasty — that is, after Dongcheon's reign. As such, Ikeuchi considered the Samguk Sagi stories of the Wei invasion unreliable.
Traveling along the coast of the Sea of Japan, Wang Qi's army made its way to the lands of the North Okjeo, assumed to be around the Jiandao area today. Despite records suggesting that the king came to the North Okjeo settlement of Maegu (買溝, also named Chiguru 置溝婁; in present-day Yanji), there is no telling what became of the king in North Okjeo, and Wang Qi's army continued further north inland. Turning northwest at the border of Okjeo and the Sushen, they traversed the Mudan River basin (either by way of Ning'an or Dunhua), home of the Yilou (挹婁) people, and crossed the Zhangguangcai Mountains (張廣才嶺) into the plains on the other side. Finally, their trek northwest brought them to the Buyeo kingdom on the Ashi River within present-day Harbin. Buyeo's regent Wigeo (位居), acting on behalf of the nominal King Maryeo (麻余王), formally received the Wei army outside their capital in present-day Acheng District and replenished their supplies. Having overextended their reach and lost sight of their target, Wang Qi's army turned southwest from Buyeo to return to Xuantu Commandery, passing by the present-day areas of Nong'an County and Kaiyuan. Upon their return, they had completed a circular trip traversing Liaodong, North Korea, and Manchuria.
Concurrently, Wang Qi sent a detached force to attack the Ye of eastern Korea since they were allied with Goguryeo. The force, led by the grand administrators of Lelang and Daifang, Liu Mao (劉茂) and Gong Zun (弓遵) respectively, started from South Okjeo and went south through the whole length of the region known as the Seven Counties of Lingdong (嶺東七縣). Six out of the seven counties — Dongyi (東暆), Bunai (不耐; also named Bu'er 不而), Chantai (蠶台), Huali (華麗), Yatoumei (邪頭昧), Qianmo (前莫) — submitted to Liu Mao and Gong Zun, while the remaining Wozu county (夭租縣), being identical with Okjeo, had already been subjugated by Wang Qi. In particular, the Marquis of Bunai, the preeminent county of the seven, was specified to have come surrendering with all his tribesmen. Liu Mao and Gong Zun's march along the eastern coast of Korea may have brought them as far south as Uljin, where the local elders informed them of an inhabited island to the east, an island which could possibly be Ulleungdo. Another inscription was erected at Bunai, supposedly to commemorate the feats of Wang Qi, Liu Mao, and Gong Zun during the second campaign; however, unlike the tablet attributable to Guanqiu Jian, this inscription has not been found.
Although the king evaded capture, the Wei campaigns accomplished much to weaken the Goguryeo kingdom. Firstly, several thousands of the Goguryeo people were deported and resettled in China. Secondly, and more importantly, the intrusions into Okjeo and Ye separated these Goguryeo tributaries from its central ruling structure and brought them back under the influence of the commanderies of Lelang and Daifang. In doing so, Wang Qi and his generals removed a substantial part of the Goguryeo economy and dealt Goguryeo a blow more severe than Gongsun Kang did forty years ago. The Ye under the Marquis of Bunai became expected to provide provisions and transportation whenever Lelang and Daifang went off to war, and the marquis himself was elevated to Ye King of Bunai (不耐濊王) by the Wei court in 247. In addition, Wang Qi's incursion into Buyeo's territory and the subsequent welcome by the hosts reconfirmed the friendly relations between Wei and Buyeo, and tributes from Buyeo to Wei would continue annually.
When King Dongcheon returned to Hwando, he found the city to be too ravaged by war and too close to the border to be a suitable capital, and thus relocated his capital to a "walled town in the plain" (平壤城, Pyeongyangseong) in 247, moving his people and sacred shrines while leaving Hwando to ruin. From this new capital, Goguryeo underwent significant reorganization, particularly in regards to its economic base, to recover from the devastation by the hands of Wei. Since the resources of Okjeo and Ye were deprived, Goguryeo had to rely on the production of the old capital region of Jolbon while looking for new agricultural lands in other directions.
The history of Goguryeo in the latter half of the 3rd century was characterized by Goguryeo's attempts to consolidate nearby regions and restore stability as it dealt with rebellions and foreign invaders, including Wei again during 259 in which Goguryeo defeated Wei at Yangmaek, and the Sushen during 280 in which Goguryeo launched a counterattack on the Sushen and occupied their capital. According to the Samguk Sagi, during the Wei invasion in 259, King Jungcheon assembled 5,000 of his elite cavalry and defeated the invading Wei army at a valley in Yangmaek, killing 8,000 enemies. Goguryeo's fortunes rose again during King Micheon's rule (300-331), when the king took advantage of the weakness in Wei's successor the Jin dynasty and wrestled the commanderies of Lelang and Daifang from central Chinese control. By this time, Goguryeo completed seventy years of recovery and was transformed "from a Chinese border state, existing mainly by the plunder of the Chinese outposts in the northeast, to a kingdom centered in Korea proper, in which the formerly independent tribal communities of the Okjeo and others had been merged."
In terms of historiography, the expeditions of the second campaign are significant for providing detailed information on the various peoples of the Korean Peninsula and Manchuria, such as Goguryeo, Buyeo, Okjeo, Ye, and Yilou. The expedition, unprecedented in scale in those regions, brought first-hand knowledge about the topography, climate, population, language, manners, and customs of these areas to Chinese cognizance, and was duly recorded into the Weilüe by the contemporary historian Yu Huan. Though the original Weilüe is now lost, its contents were preserved in the Records of Three Kingdoms, where the reports from the Goguryeo expedition are included in the "Chapter on Eastern Barbarians" (東夷傳, Dongyi Zhuan) — considered the most important single source of information for the culture and society of early Korean states and peoples.
十二年冬十二月王畋于杜訥之谷魏將尉遲楷名犯長陵諱將兵來伐王簡精騎五千戰於梁貊之谷敗之斬首八千餘級. Ikeuchi (1929) questioned the authenticity of the Wei invasion record since the Wei commander was recorded in Samguk Sagi as Yuchi Kai (尉遲楷). Ikeuchi reasoned that since the Yuchi surname was not mentioned in Chinese records before the year 386, the Wei commander's name might be anachronistic. See Ikeuchi 1929 : 114.