It refers to that around 450 AD, the emperor of the Southern Song Dynasty rushed to the North and went to Henan, trying to expel the nomadic regime in the north (sealing the wolf to occupy Xu is a metaphor), but failed. Later, Emperor Tuoba Tao of the Northern Wei Dynasty (the comment area said that the Northern Expedition was "Xiongnu", and I was really drunk) organized a counterattack, directly hitting Guabu Mountain on the north bank of the Yangtze River, facing Nanjing across the river, and Liu Yilong looked north in Nanjing. Later, Tuoba Tao withdrew his troops and destroyed the city and slaughtered the people in Huainan. It is recorded in history that "the swallow returns and nests in the tree"-people die, the house is gone, and swallows can only nest in the tree.

The object of the Northern Expedition was not the Xiongnu, but the Northern Wei Dynasty of the Tuoba Department of Xianbei nationality. The location of the Northern Expedition was not Mobei, but the Central Plains.