Autumn Counteroffensive
The Autumn Counteroffensive, also known as the September Counteroffensive Plan and the Two Provinces Campaign, was a major military offensive undertaken by Imperial forces after the Autumn Offensive. It was the last Imperial offensive to make territorial gains, which lifted morale among the Imperial troops. The inconclusive confrontation at Jingye and the Allied victories at Munghae and Gyeongpo prompted the Imperial retreat further north. The result of the counteroffensive led the Imperial troops to term the operation the Last Happy Time (Quenminese: Thời gian Hạnh phúc Cuối cùng; Archadian: L'Ultimo Momento Felice; Ruzhite: Последнее счастливое время, Posledneye schastlivoye vremya).
The partial strategic success of Gangwon-Ragye Offensive left the Allies to regroup their formations, allowing the Imperials to solidify their current lines from Haedong and Yangseong. The Imperials were then supplemented by troops from Churuongchandat, who were previously on reserve to maintain security in Northern Joyonghea. As preparations were being made, Hồ Danh Sĩ Quốc temporarily re-organized the Imperial formations into the Combined Imperial Front of Joyonghea comprised of the Left and Right Wings, commanded by Ông Thao Pin and Quách Khánh Thắng Due, respectively. Taking note of the current Allied and Imperial positions, and the strategic terrain around Yangseong, Quốc intended to let the Allies take the offensive, and slowly lure a portion of the Allied forces facing the Left Wing at Yangseong on grounds near Uijeongsok to prompt their retreat and flank the Allied attack on Right Wing at Haedong in order for the Imperials to move southward to retake lands lost during the last offensive. The Allies attacked Haedong on 25 September and Yangseong a day later. The Right Wing maintained a staunch defense and repulsed Allied offensive manuevers despite several setbacks, and the Left Wing inflicted heavy losses onto Allied forces that prompted their retreat; a contributing Imperial move that led to the Allied retreat from Yangseong was the engagement of 105th Infantry Division, the 91st Infantry Division, and the 3rd "Steel Tiger" Division against the ZANAKs and Joyongheans at Uijeongsok. The Right Wing pushed forward towards Jingye, while the Left Wing pursued the Allies until Poneung on 9 October. Quốc then ordered Pin and Due to press forward onto the two cities so to accelerate the threat towards Yeolcheon, instigating the Battle of Jingye and the Battle of Poneung and Chosuji. The Left Wing unsuccessfully attempted to dislodge the Allies at Jingye, while the Right Wing scored a tactical victory the latter city and town, but with heavy casualties. After analyzing the current situation, Cheon Sang-ji made the decision to leave a relatively small force at Munghae in hopes of inflating Quốc's confidence to move forward. The gamble was successful, and Cheon was able to force the Right Wing's advance back at the subsequent engagement on 25 October. Quốc ordered Pin to send a detachment to Munghae for assistance, but this force was stalled and repulsed at the Battle of Gyeongpo on 27 October. On 28 October, Quốc gave the order for the entire Combined Imperial Front to retreat further north.
The failure of the Imperials to completely regain the Gyeongsang and Ulsan Provinces meant that the Imperials would never again mount another offensive action, and remain on the defensive until the end of the war. The Allied victory at Munghae and Gyeongpo effectively solidified their liberation of the aforementioned provinces, and prompted advance onto the South Gyeonggi and Hamhung Provinces. Moreover, it saved Yeolcheon from undergoing another confrontation. The Counteroffensive observed notable hallmarks: Yangseong was the second worst defeat and the worst suffered by the ZANAKs and Joyongheans in the conflict; and, Munghae was the military move that spared the Allies of another humiliating setback, aptly termed by military historians as "Cheon's Gambit".