In this time period, there was the rise and fall of several rulers. After the Han dynasty fell, there was the rise of three kingdoms--Shu Han, Cao Wei, and Dong Wu. Then, in 265, the Jin dynasty started. In 280, the Jin unified China for a short period, until 316. Then there were small city states in the north, and the Eastern Jin in the south.
In 357, Fu Jian started conquering cities in the north, and in 383 tried to defeat the Jin at the Battle of the Fei River. Even though Fu Jian had a much bigger army, the Jin defeated them. At that pont, Fu Jian's cities started falling away.