Han in 979, Emperor Taizong took advantage of the momentum and launched another military campaign against the Khitan-led Liao dynasty. In May 979, Emperor Taizong embarked on his campaign from Taiyuan and took Zhuo and Yi Prefectures easily. He besieged Yanjing (present-day Beijing) after the success. However, the siege failed when the Liao defending general Yelü Xuegu defended the fortress firmly. Concurrently, Liao reinforcements led by Yelü Xiuge arrived from the Gaoliang River region, west of Yanjing. Emperor Taizong ordered his army to attack the reinforcements. Initially, he received reports that the Liao army was suffering heavy casualties. He ordered a full assault on the Liao army as he thought that the whole battle was under his control. Just then, Yelü Xiuge and Yelü Xiezhen's armies attacked from two sides. Yelü Xiuge concentrated on attacking Emperor Taizong's main camp. Emperor Taizong was shocked and evacuated from the battlefield. During the evacuation, the Song army was divided and obliterated by the Liao cavalry. Amidst the onslaught, Emperor Taizong fled towards Yi Prefecture and arrived there safely with his generals protecting him. He sustained an injury from an arrow and was unable to ride on his horse and had to travel by carriage back to Ding Prefecture. Emperor Taizong ordered a retreat after that. The Song army was without a commander as Emperor Taizong was separated from his troops. The troops suggested that Emperor Taizu's eldest son, Zhao Dezhao (Emperor Taizong's nephew), be the new emperor. Emperor Taizong's suspicions were raised when he heard that and eventually he ordered Zhao Dezhao to commit suicide. The Battle of Gaoliang River was significant as it was one of the major contributing factors to the Song dynasty's decision to adopt a defensive stance. The early Song army suffered its first major defeat in battle. Meanwhile, Emperor Taizong was also troubled by the possibility that Zhao Dezhao would launch a coup. After the battle, Emperor Taizong personally inspected and focused more on the development and strengthening of his military forces. He ignored his subjects' advice and regarded state affairs as of lower importance. He also limited the power and control that the imperial family and military officers had over the army. Second campaign against the Liao dynasty After the death of Emperor Jingzong of Liao in 982, the 12-year-old Emperor Shengzong of Liao ascended to the throne of the Liao Dynasty. As Emperor Shengzong was too