How's the U.S. Government performed over the last 200 years?

[John21]

Granting that the purpose of a government is to protect, preserve, and promote the intrests of its citizens - how has the US Government performed over the last 200 years?

I'd also ask that you consider the following as givens:
1) Americans enjoy one of the highest standards of living compared to most countries.
2) Military wise, the U.S. is the only super-power on the planet. I'm not saying, morality wise, being the baddest cat in the alley should be a priority, but since we're all poker players, lets just call it having a huge chip stack.

With specifics aside and being as objective as possible - how'd they do?