Reunification and War with the Liao
The Last Independent States
Taizong completed the reunification his brother had begun. In 978 the rulers of Wuyue and of the Zhangzhou and Quanzhou region on the south-east coast surrendered their territories peacefully. In 979 he led the campaign against the Northern Han himself. Its capital, Taiyuan, was besieged, a Liao relief army was driven back, and the Northern Han ruler surrendered. The conquest brought the Five Dynasties and Ten Kingdoms period to a close. The old city was afterwards razed, and a new Taiyuan was built nearby.
Gaoliang River, 979
Straight after this victory, Taizong marched on Youzhou (modern Beijing), the chief city of the Sixteen Prefectures, a band of northern territory held by the Khitan Liao. At the Gaoliang River in 979 his army was routed and the emperor, wounded, escaped with difficulty. It was the first great defeat of the Song army, and it pushed the dynasty towards a defensive stance in the north.
During the confusion some officers had proposed making Taizu's son Zhao Dezhao emperor. Taizong's suspicion of his nephew afterwards is well recorded, and Dezhao took his own life later the same year.
The Yongxi Campaign, 986
In 982 the Liao emperor Jingzong died and was succeeded by his young son, Shengzong, with the Empress Dowager Xiao as regent. Seeing an opportunity, Taizong launched a new offensive in 986, during the Yongxi era. Three armies were sent to converge on Youzhou from different directions.
The eastern army under Cao Bin took Zhuozhou but had to withdraw for lack of supplies. When it advanced again, poorly coordinated with the other armies, it was caught by Liao forces under the Empress Dowager and the general Yelü Xiuge and almost destroyed at Qigou Pass. The western army was also forced back, and its general Yang Ye was captured and died in Liao hands. The campaign ended in failure, and the frontier remained hostile until Taizong's successor, Emperor Zhenzong, agreed the Treaty of Chanyuan in 1005.