Strategic Background
After Gongsun Yuan's Liaodong regime was annihilated by Sima Yi, Caowei's northeastern boundary advanced directly to the Yalu River line, bringing Wei into direct territorial contact with Goguryeo. King Dongcheon of Goguryeo exploited the vacuum left by the collapse of the Gongsun clan to actively expand northward, repeatedly raiding Wei's borders and cutting the communication links between Liaodong and the two commanderies of Lelang and Daifang. From Caowei's perspective, if this "neighboring state growing stronger" situation were not checked promptly, the newly integrated northeastern defensive line would again become unstable. By the fifth year of Zhengshi, the governance pattern in which Cao Shuang and Sima Yi jointly held court power had been established; the Inspector of Youzhou, Guan Qiujian, was granted full authority to handle Goguryeo affairs — this campaign was therefore simultaneously a frontier operation and an extension of central politics into the borderlands.
Deployment
The Wei forces numbered over ten thousand cavalry and infantry, supplemented by the commandery troops of Lelang and Daifang as flanking support, with the overall objective of "rapid advance, deep strike at the enemy's lair." Tactically the plan used frontal engagement as a lure and a secret crossing by elite troops as the point of rupture. King Dongcheon of Goguryeo concentrated twenty thousand crack troops to give battle, fortifying along the terrain of the Feiliu River, Liangkou, and similar features, while also relying on the steep heights of Wanducheng as the last line of defense. This was the traditional response of trading terrain for strategic depth, but it underestimated the engineering capability and maneuverability Wei's forces brought to long-range expeditionary warfare.
Key Decision Points
The decisive turning point came at the siege of Wanducheng. The Wei army kept the Goguryeo defenders' attention occupied with a frontal feint while covertly selecting climbers among the elite troops who scaled the city wall from the northwest cliffs by night, killed the sentries, and opened the gates, after which the main force poured in. This maneuver closely resembled He Qi's "engineering surprise assault" on Linlishan in earlier times — the terrain itself could not be changed, but a defender's dependence on that terrain could be overcome through engineering. King Dongcheon was forced to abandon the city and flee east to Eastern Okjeo; Wei forces then hunted down his remaining forces in the city and engraved a commemorative stele recording the victory of the first campaign. In the second campaign the following year, Guan Qiujian held Wanducheng as his command post while dispatching Wang Qi deep into Okjeo to pursue King Dongcheon; troops from Lelang and Daifang swept through the tribes affiliated with Goguryeo further to the south — the campaign took on the advanced form of "center holding firm, four-way mobile strike."
Outcome and Legacy
After the two campaigns ended, Guan Qiujian, Wang Qi, and others erected commemorative steles at the site of Guonei Fortress; fragments of the inscriptions survive to this day, constituting important physical evidence for the study of the Weijin-era history of the northeastern Asian frontier. In military terms, the Goguryeo regime was driven nearly to extinction; King Dongcheon perished in Okjeo, and his descendants did not dare to expand westward on a major scale for decades. In political terms, Caowei's governance of Lelang and Daifang was restored, and through this region the tribute-mission routes to the Korean peninsula and the Japanese archipelago were further regularized — it was only after this regional geostrategic space had stabilized that the reception protocol for the envoys sent by Himiko, Queen of Yamatai, during Emperor Mingdi's era could be conducted. This expedition also became the political template for the later Western Jin's management of the northeast: use an engineering surprise assault to take the capital city, mark the victory with a commemorative stele, and maintain order in the surrounding area through coordinated commandery troops.
Counterfactual Analysis
Had Guan Qiujian opted for prolonged siege rather than the surprise assault on Wanducheng, the campaign might have stretched into winter, at which point Wei's supply lines would have become untenable and Goguryeo would have gained time to recover. Had Caowei not promptly established normalized governance of Lelang and Daifang after this victory, the fruits of the expedition would have eroded rapidly with time. From a longer vantage point, the greatest long-term value of this expedition lay not in its geographic gains but in establishing a paradigm: a Central Plains dynasty could use an elite expeditionary force of slightly more than ten thousand men to conduct a strategic-level sweep deep into northeast Asia. This paradigm was repeatedly borrowed in later ages — from the Sui-Tang campaigns against Goguryeo to the early Ming's Liaodong operations — and their underlying logic can still be traced back to this campaign in the fifth year of Zhengshi.