Athenian Democracy
185 years (507-322)Roman Republic
402 years (509-107)Royal England (Common Law)
427 years (1215-1642)Imperial Parliamentary United Kingdom
259 years (1688-1947)First French Republic
7 years (1792-1799)Second French Republic
4 years (1848-1852)Weimar Republic
14 years (1919-1933)Union of Soviet Socialist Republics
72 years (1917-1989)United States of America (voluntary)
73 years (1789-1861)United States of America (involuntary)
139+ years (1865-2004)
I’m not saying that the world will come to an end when the US system of government changes and/or collapses. My best guess is that it will become an integral part of an North-Central American superstate in the mode of the European Union, which will eventually be a state in the federal world government. And, as in many of these previous cases, most people may not even notice the change; indeed, future historians may well decide that the Constitutional USA ended long before 2004, perhaps as early as 1865 when the Union ceased to be voluntary. (I don’t want another Civil War discussion; causes aside, the result is not debatable.)
Modern England is a decent place to live, after all, but it’s not the center of world power it once was under the Imperial Parliament. And one could even argue that for the average sybarite, Imperial Rome was a more entertaining place to live than its Republican predecessor. But then, there’s always a few crazy Old Republicans who have no desire to live under the rule of Augustus Caesar.