Greed and a lust for power. The same things that ended the Roman Empire are sending the Imperial Presidency into a tailspin.
Lucius Cornelius Sulla, Dictator, is looked upon by many as the beginning of the end. Keep D&D Civil.
From a historical standpoint I would disagree. The Roman Empire lasted for about 5 centuries after the Republic had ended and reached its height of power and size under Emperors. I'm not saying that is something we should strive for just making the point that things weren' all bad under Emperors.