The Roman Empire was over-extended, and that's the main reason it collapsed. It basically got too big. On the other hand, no matter how powerful you are there is always going to be someone else more powerful looming, waiting for you to make a mistake so they can swoop in and pick up the pieces.
This isn't directly responding to the question posed by moocow554, but asking a related question. Look at the list of factors contributing to the fall of empires as provided in post #3 and think about the current set of circumstances and conditions in the USA. Anyone else see any similarities? Any reasons to feel some apprehension about the coming years?
I think when it comes to the Roman Empire, we need to remember the way that it stretched across vast geographical tracts of land. Although its system of administration meant that it could function effectively, it also meant that the Empire was made very vulnerable to attack from an increasing number of different angles. One reason that the Roman Empire thus declined was the impossibility of trying to defend itself against all possible threats on an ever-increasing geographical border.
As one of the previous posts mentioned, the decline and fall of the Roman Empire occurred primarily from its wide extension and expansion of lands, combined with a new group of powerful armies from within and without. The western empire collapsed in the 5th century, in part because of attacks by migrating groups; and the eastern empire survived for another thousand years before becoming part of the Ottoman Empire (or Byzantine Empire).
Many people have argued that empires collapse for a number of reasons that tend to be common and overlapping in the histories of different imperial regimes. Such causes often include the following:
- Over-extension, especially militarily. Some empires (the Roman empire, for instance) conquer so much territory that defending it all becomes nearly impossible.
- Failure to assimilate conquered nations and cultures into the culture of the imperial power.
- Imprudent, improvident spending.
- A steady diminishment of confidence in, and commitment to, the values that caused the empire to expand in the first place.
- The loss of the original talented, charismatic figure (such as Alexander the Great) who helped lead the imperial expansion in the first place.
- Military losses, often at the hand of allied enemies (as with the Napoleonic Empire and the embryonic empire that Hitler had begun to establish).
- The sudden arrival of some newer, stronger, imperialistic force, as in the case of Spain's conquest of the Inca empire.
Assyria started out as a civilization that practiced agriculture because of abundant rainfall and developed trade that exchanged copper ore for textiles. They had ongoing conflicts with the Hitties and Amorites. In the final stages of the empire, Assyria conquered Egypt and thereafter, having overextended the treasury and manpower, their collapse came quickly when Nebuchadnezzar of the Chaledeans and Medes came to power.