When looking for a “type” of government to base the new America on, what successful government examples did our Constitution writers have?
It would seem that the great Roman Empire outgrew itself. After its heyday when monarchial rule by Julius Caesar and his powerful armies led to its great expansion, Rome slowly disintegrated into factions where the wealthy ruled the poor (Corpus Juris Civilis), the army became lax, liberal philosophical thought gave way to lower moral standards.
After its split into a Western and an Eastern Empire, one can only imagine the conflicts arising from lack of communication: 1) standardization of two separate armies, 2) different philosophies of life, 3) differing religious beliefs, 4) different governmental rules for its peoples, especially those whom the Romans had subjugated and sometimes enslaved. “Italy and the provinces of the empire returned to a less advanced state of the social division of labor” (The Social and Economic History of the Roman Empire).
Some historians claim the barbarian invasions slowly destroyed the empire. My personal feelings are that these invasions were successful because Rome had already become internally weak. As a result, people gathered around the manorial barons who promised them protection and at least, minimum subsistence (Human Action: Observations on the Causes of the Decline of ancient civilization).
The decline of so many great empires is similar to that of the Romans. The far reach of Islamic civilization remained at an apogee for centuries. But as interpretations of Islam slowly resulted in various sects and sub-sects, philosophies of life became disparate. The thinking, morality, government, religion, and economy changed.
To add to this, as the West reared its head once again, colonialism of territories held by Muslims led to a certain materialism that slowly strangled Islamic Civilizations (CounterCurrents.org). Add to this the size of the empire, the variety of conquered peoples, the invasion of the Mongols, and we have a Rome reoccuring.
I’m sure that the rise and fall of many civilizations in ancient times and in a more modern era followed a rather predictable path from rise, to apogee, to decline: Ancient Greece, Egypt, Mesopotamia, India, Britian, etc.