In this paper, we discussed the war situation between 666 and 667, which is the first half of the Goguryeo War (666-668). Emperor Gāo zōng of the táng Dynasty invaded Goguryeo to save Namsaeng on June 7, 666. Namgeon, who ousted his older brother, Namsaeng, and became Goguryeo's new ruler, was stationed in Yosu with 150,000 troops directly to cope with the táng's dispatch. In September 666, Goguryeo and táng troops fought one battle in Yosu, and táng troops returned without securing Namsaeng's safety.
Later, in October 666, the táng Dynasty invaded Goguryeo with a large force. The following year, from January to February 667, the táng army's strategy to conquer Yosu was to secure the Sūzǐhé basin and the domestic area after the capture of Sinseong, and to march to Pyongyang by crossing Yalu River. Goguryeo's Sinseong army fought a fierce battle for 8 to 9 months against the táng army's invasion, but it fell on September 14, 667 due to internal betrayal.
After that, the táng army dispersed its power, and Lǐjī advanced south to the Yalu River area, and Qibi Heli, Pángtóngshàn, gāo kǎn, and xuērénguì defended Sinseong, taking control of the Soja River basin and the area of Gooknaesung and securing the personal safety of Namsaeng. Goguryeo troops blocked the Yalu River Doha and prevented the expansion of the front line against the táng army of Lǐjī who marched into the Yalu River area.
After that, the Tang army marched to “Ansiseong” to find a new way out. However, Goguryeo's troops saw through this and blocked the Tang army's capture of “Ansiseong” by surprise. Since Goguryeo succeeded in the defense of “Ansiseong”, it can be seen that it also had the effect of defending “Gunanseong” and “Ogolseong” and blocking the Tang army's operation to carry out the Yalu River.