[Why] In late Eastern Jin the aristocratic clans grew thoroughly corrupt, the Sun En uprising broke out within, and local warlords contended without. The general Liu Yu of low-status origin leveraged outstanding war records to gradually grasp Eastern Jin power. [What] Liu Yu deposed Emperor Gong of Eastern Jin and proclaimed himself emperor, founding the Liu Song and formally ending Eastern Jin. He vigorously purged the old great clans, vigorously restructured internal administration, and raised the curtain on Southern Dynasties history. [Who] Liu Yu was an outstanding low-born military commander whose two northern expeditions retook Luoyang and Chang'an, winning broader defensive depth for the South. The last emperor of Eastern Jin became a sacrifice to the political transition. [How] The founding of Song marked the start of the decline of decayed aristocratic clan politics from Wei-Jin onward, with power shifting toward the low-born warrior class. It became the violent point of departure for dynastic succession in the Southern Dynasties.
Why
The historic event of Founding of Liu Song represents a key developmental peak of the Huaxia dynastic system. The rise of military men from humble origins and the decline of noble clans. By establishing this moral or administrative benchmark, it continues to shape the structural and philosophical fabric of ancient Chinese statecraft.