The tragedy of Rome is that it could not maintain what was once a very powerful unified force. While citizens might still have been loyal to Rome and their citizenship, the emperors appear to hardly have been so, and indeed, they appeared both increasingly irrational and selfish in their actions, rather than acting as leaders that would continue their powerful expansion throughout the world. The reason for Rome's longevity lies in the unity, loyalty and mutual support between citizens and their rulers. When this began to collapse,...

The Collapse of the roman empire - Military Aspects. Late Antiquity in the Mediterranean. http://www.nipissingu.ca/department/history/muhlberger/orb/milex.htm
Muhlburger, Steven. Ideology, Identity, and Empire - the Romans

http://www.nipissingu.ca/department/history/muhlberger/orb/OVC1S6.htm

Ross, Kelly L. The Origin of Philosophy: Why the Greeks? http://www.friesian.com/greek.htm#why