As an aside, For all those who talk about corruption and getting money out of politics I suggest reading Federalist 10 by Madison. Its a deep analysis of a need for a republican democracy. Any government that depends on human virtuousness will fail. The only way to have a sustainable government is to have strong checks and balances and putting multiple factions with different interests against one another.
All governments fail, it’s only a question of when. The stability of the US is in no small part due to its geography and natural wealth. Having two oceans on each side and more arable land than you know what to do with is far more of an asset anything written on paper. It seriously reduces the threat of external and internal conflict, and the US got this for a song.
Further, there’s a strong argument to be made that the US did not last this entire time. The centralization that happened after the Civil War created a fundamentally different government than was created in 1789. Through the process of incorporation, constitutional amendments were enforced on states which created a far more uniform country.