I just gave you examples of EU inner workings. They are also incredibly interconnected, almost as much as the US. Still, they have institutions to give some power to the smaller entities/states. The US institutions are not made the way they are because "people could not travel far enough in a day", they are made as such to provide checks and balances. As an European living in the US, I feel like you have more stable mechanisms that work better than even the modern EU.