The success of empires did not necessarily equate to the success or the flourishment of its citizenry. Therefore, they ultimately failed.

>>The ultimate success of the USA, IMHO comes straight from the Declaration of Independence --
>
>Historically, the successful empires had little of "Life, Liberty and the pursuit of Happiness". For instance, the USSR went toe-toe with the US technologically and militarily for a long time. Unfortunately their economy was in shambles.
>
>Other examples of Empires with little liberty:
>- Roman
>- Chinese
>- British
>- Japanese
>
>The US seems to be a libertarian anomoly. Though this doesn't dispprove your statement, perhaps there is another thing in common that all succesful empires have had. Some that the US also has.