Hmm, according to all kinds of measurements, indexes, etc. the most democratic, free, hight standard of living countries reside in northern Europe. Most of them don't have much military. So somehow this comment is pretty flawed.
The US once was the most free countries and indeed helped and inspired others, but that was more than a hundred years ago. The problem is while other countries emerged (possibly because of mistakes, losing wars, being split, reunited, etc.) the US has had a few problems that got them stuck.
I think and it's just my opinionated explanation. I might be completely wrong, but I think the biggest problem for the US where the two world wars and the cold wars. Basically it made the country/government learn that espionage, military, etc. is a good thing, because they only win. They win no just like the war itself, but they win control of people, they pretty much unite them, but even that is not all. The military system allows the US to do what other countries do with welfare. They reinvest tax money, the out it into families of veterans, have a huge military industry from weapons to mercenaries. It works. Just like it allows them to do heavy espionage in the name of national security.
On the other hand there is expensive education or bought education (VISA policies), not the best health care system, still a lot of weird stuff, like death penalty (an example of how the US is stuck), bad infrastructure (streets, internet, etc.) and a lot less liberties or equal treatment of sexes and "races" for example.
This is something that stabilizes the US. I don't know, in a way it is a valid thing. Stability is good and there is pretty much no country that does so well that it should judge the US for that.
Another problem is that they tend to do overpropaganda, so they can't really change. They had stuff like the cold war, so communists (Russians/Chinese) people are super evil. Also there were no other reforms. The two party system where both have pretty much opinion. That's no way of choosing. For example the death penalty thing I mentioned. Republicans are pro, Obama is pro. So no movement in sight.
The US is also stuck in nationalism. Like really, do you know any other developed country that is so much into flag waving and where everyone is like "Mall of America, Bank of America, X of America"?
Like I said. It's not bad. It brings stability, which is something people want, but it also means that progress simply stalls.
In this regard the US is actually quite the same as China or Russia. Big countries, which pretty much always the same government, lots of propaganda, lots of nationalism "the others are all bad (or envious)", death penalty, secrecy, lots of military investment, our country is the best, etc.
It might also be a thing of size. There have been political-philosophical works about this, partially with practical implementation (The Breakdown of Nations).
However, as history tells us (see various empires) these things break down in bad ways. Sadly it usually means the next nation will become like this and won't be any better at all. And yeah, I am not a friend of nations and stuff, but I am realist enough to know, no matter how long the US remains like that (yeah, I think it is trembling, but I think it's far from falling) or whatever, this isn't going to change. I also don't think there can be any kind of utopia. It would be really cool if people just abandoned stuff, but no matter how wrong communists are. There is one thing they got correctly (but usually still don't live after, else they wouldn't be communists): It might be nice for a while, when everyone understands how shitty things were and how nice it is to just live together, but people forget that and then it really starts from the beginning.