And Caesar knew that, he was a citizen of the NCR, which is why he created Caesar's Legion. It's really interesting when you think about it, and not just go "FOR AMERIKUHHH".
But the Roman Empire fell as well. Why not choose a totally different path if he thought pre war societies were bad.
Slavery, conquest be sheer force, and keeping order by killing have already been done and failed.
Everything will fail, because humans are not capable of governing themselves on a grand scale in anyway. It might work for hundreds of years, but sooner or later one way or another it will end badly.
In all reality small groups is probably the best way, because every one is more likely to have a say. The problem with that is they will be forced to fight with other small groups, or will be destroyed or swallowed up if a large group rolls through.
Humans are just incapable of toleranting each other for long derations.