Eau contrair....(yes it's a pun)
<Re: Rome was not a nation or a country.
Rome was a city and an Empire."
Depends on what period you're refering to.
Rome started as a Republic.
It defeated it's nearly equal rival (Carthage) it it's local sphere, the Med.
It later expanded and acquired what were essentially colonies.
It's not a great literal analog for the U.S. but it is a similar case where something with promise became obsessed with power and security and suffered cultural ferment till the barb showed up.