After the establishment of the Song Dynasty, Zhao Kuangyin did not completely unify the world, and there was Li Yu in the south. Even if it is annexed, it will take some time to digest. Otherwise, once the front forces are tight and the rear defense is empty, those who have two minds are likely to take the opportunity to fight back. To the west is Xixia, which took the opportunity to grow and develop. In the north, in addition to the Great Liao established by the Khitans, there is also the Northern Han Dynasty. In this case, even if these opponents are defeated one by one, the situation will be consolidated. But if it fails, it is likely to be besieged by these opponents, and it is likely to be defeated and flee like Liao Shizong. As for the Khitans, most of them are monolithic. Unless they meet a sleepy emperor like Liao, they occupy sixteen states of Youyun, and the terrain is high and high, so they can use cavalry flexibly. This is their advantage, so Zhao Kuangyin also dare not go to the Northern Expedition easily.

Zhao Kuangyin once fought against the Northern Han supported by the Khitan, because at the beginning of the founding of the People's Republic of China, he found that he could not occupy the Northern Han, so he settled for the second best and supported the Northern Han as his puppet. Only by defeating the Northern Han Dynasty first can we be qualified to fight against the Great Liao Dynasty. This process is not only slow, but also takes some time to cultivate students and improve their interest. After all, the slogan shouted at that time was the disarmament of ten thousand people in the Northern Song Dynasty. After the Five Dynasties and Ten Kingdoms War, people's anti-war sentiment was very high, which is also an objective factor.

When Zhao Kuangyin's yellow robe was added, it was in Liao Dynasty. If he hadn't usurped power, he could really attack the north with justification. But at this time, he can only consolidate his rights and avoid civil strife in the Northern Song Dynasty. At that time, many forces supported Chai Rong, and even Zhao Kuangyin had to be kind to Chai Rong's descendants, which also made him lose the opportunity to attack the Liao Dynasty.

It was not until Zhao Guangyi succeeded to the throne that the power of Da Liao was held by Empress Xiao Zhuo. He thought the other side was not afraid, but he suffered a big loss. This also objectively shows that Daliao has a rich background. When the battlefield is in the Central Plains, Zhao Kuangyin can still take advantage of this. But the battlefield has reached the other side's territory, and they have been running sixteen states of Youyun for decades, which is deeply rooted and hard to beat.