Just noting that Carthage and Venice were destroyed by outside forces. Sure Carthage would most likely have collapsed or otherwise become a dictatorship a la Rome but who knows maybe they wouldve reformed. As for Venice that's basically impossible to know, they reformed their government so many times in their history so as to keep power hungry assholes from getting power that who knows what wouldve happened had they survived into the 19th or even 20th century.

Though regardless I suspect the US may not have even 10 years left in it, hell it may not even have a year left in it if shit hits the fan badly enough.