Military Power Shift and the Overthrow of the Roman Empire

In the history of the Roman Empire,there was a military power shift from the Senate to a group of people,then to a few people, and at last to the emperor.This shift enabled the Roman Emperor to take the military and political power into his own hands.However,with no strict inheritance system,the power used to be out of control,which caused political confusion,frequent civil wars,heavy taxes,economic depression,corruption of the army and slackness of national defense.All these factors destroyed the empire.