In the second year of Yuanxi (420), Emperor Wu forced Sima Wende to abdicate, that is, he proclaimed himself emperor, with the title of Dasong, and changed to Yuan Yong Chu. When the Eastern Jin Dynasty perished, China began to enter the Southern and Northern Dynasties.
This means that Emperor Wu of Song adopted the name abdication, which represents justified. Of course, he can't go too far. Now that he has won the throne and destroyed the ancestral grave of the former emperor, the whole world will accuse him.