1) The empire was too big to control: This led to a strain of military supply, and the amount of troops in an area. IF all the places rebelled at the same time, they were not able to contain them. 2) Civil wars: East vs West. The Civil war also weakened the Empire as they usually were trying to beat the other side up instead of protecting their borders 3) Others: corruption, uprisings, protests, attack from outside, taxes were to much of a burden for their citizens, all sorts of other things
