Upvote:-2
China is usually said to be the longest running polity, though of course they have had periods where government broke down, for example during the warring states period and more recently, when Communist China drove the Nationalist forces under Chiang Kai-Shek from the Chinese mainland to Taiwan.
Upvote:3
The British have had a stable government from 1688 (arguably from the 1660 Restoration) to the present, a run that predates the U.S. Constitution ratification in 1788 by 100 years, As both forms of government continue in tandem, the former has clearly run for a longer extent than the latter.
As both governments are also Representative Democracies, the U.S. cannot even claim to be the longest running instance of that governmental form.