This is a big question. In short, during the Eastern Jin Dynasty, the imperial power was weak, and the central and local governments were controlled by high-ranking gentry, such as the Wang family, Yu family, Huan family, etc. The secondary military nobles are the main military pillars of the regime.
For details, please refer to Mr. Tian Yuqing's book "The Politics of Eastern Jin Dynasty" and the long article "The Politics of Family" written by Mr. Zhu Zongbin (included in the seventh volume of "General History of China" edited by Bai Shouyi)