I think you are just wishing it were so, because you don't like what America is trying to accomplish on this planet I admit that I am afraid of one center of power for the whole world. When such concentration of power occurs, without multipolar checks and balances, how the freedom can survive?
When the city state of Rome conquered the Mediterranean world, she lost her liberty and got absorbed by the Empire. Is the historical mission of America to unite the whole world?
Liberty in America remains robust. Rome never had anything remotely like American liberty, or American ideology, or the economic productivity and the independence of those who generate it, on a very widespead basis, to support it. In short, Rome did not have much of a productive middle class, in part because the technology of the time could not support it. It's empire was supported by the spoils of war. America makes no profit economically on spoils, either of war, or otherwise. Indeed, other than in keeping the international economic system going, which increases the standard of living of each and every one of us, it is an economic loser.
The whole analogy is ludicrous.