After Hu-Han/後漢 dynasty collapsed, the Gongson-shi/公孫氏 regime newly came to present itself as the new ruler of the Liaodong/遼東 region. This kind of power shift clearly affected the internal stability of the Koguryo dynasty, as subordinate groups such ...
After Hu-Han/後漢 dynasty collapsed, the Gongson-shi/公孫氏 regime newly came to present itself as the new ruler of the Liaodong/遼東 region. This kind of power shift clearly affected the internal stability of the Koguryo dynasty, as subordinate groups such as Sosumaek/小水貊 and Dongyae/東濊 started to waver, causing the region to be de-stabilized. Yet, the Three dynasties of China continued to fight each other viciously through the 220s, so they were in no position to launch a solid Eastern policy at the time. Thanks to the situation, the Gongson-shi regime was able to establish a strong power base throughout the region, without being interrupted.
On the other hand, Koguryo was out of diplomatic options to maintain the Gongson-shi regime in check. So, the Koguryo government chose to designate an emergency military defense fortress as the temporary capital city, and construct a series of mountain fortresses along the right side(右岸) of the Hun-jiang/渾江 river in a fairly concentrated fashion. These military efforts of defensive reinforcement were part of the overall response to the military threats of the Gongson-shi forces, but it was also meant to be utilized in maintaining internal security of the dynasty, keeping the subordinate groups in place.
Since the end of the 220s, the Oh dynasty ruled by the Son House('Son-Oh/孫吳') and the Chok-Han/蜀漢 dynasty formed an alliance, and immediately launched an aggressive Northern campaign. Especially the 'Son-Oh/孫吳' tried to launch a joint operation with the Gongson-shi House and attack the 'Joh-Wei/曹魏'(the Wei dynasty ruled by the Joh House). The Oh dynasty attempted to establish a military installation in the Liaodong region by dispatching a huge military there, but the sudden changes in the Gongson-shi House's position prevented the efforts from being ever implemented.
The relationship between Koguryo and Son-Oh was initiated, as several members of the Son-Oh delegation that was sent to visit the Gongson-shi regime fled to Koguryo asking for protection. At the time, the Son-Oh government was outraged by the betrayal of the Gongson-shi regime, so it was easy for Son-Oh to establish a joint front against the Gongson-shi regime with the Koguryo dynasty. But in 234, even before such diplomatic relationship between both entities had the opportunity to be settled, Jaegal-Ryang of the Chok-Han dynasty died, and his death seriously endangered the joint Northern campaign which was based upon the joint efforts of Chok-Han and Son-Oh.
Taking advantage of the situation, the Joh-Wei launched its own Eastern campaign. Apparently, Koguryo also favored such launch, as the Koguryo government beheaded the Son-Oh emissaries in 236, sent their heads to Joh-Wei, and joined the Joh-Wei dynasty's conquest of the Gongson-shi regime in 238. But Joh-Wei chose to pursue a separative-ruling policy even more strongly than the Gongson-shi regime. Such policy was a direct threat to the Koguryo security. In response to such threat, Koguryo launched a preemptive strike against the Seoanpyeong region in 242. Joh-Wei also retaliated upon all fronts, and maintained the separative-ruling policy.
These series of events that happened during the early half period of the 3rd century, significantly changed the foreign policy of the Koguryo dynasty. But the Koguryo dynasty designed its own military defense system with taking the disturbances that might occur among the subordinate groups into account, and implemented it throughout the outskirts of the central, so Koguryo was able to restore control of the central areas, and deflect additional assaults of the Joh-Wei dynasty rather efficiently. Koguryo also took advantage of the situations when the foreign policies of Joh-Wei or West-Jin showed any weaknesses, to reinfor its control over the subordinate groups throughout the region.