Currently, the state of the United States economy is so bad that it is almost impossible to believe that the country will successfully emerge from the turmoil. Along with the possibility that our economy will collapse, there are several other issues that cause concern, when looking at the longevity of the country, including the entry into more and more wars, and the constant contentions over social issues.
Think about it, we are a lazy generation, no matter how you put it. Instead of craving our writing into stone, we type it on a key board. In past societies world-changing inventions like languages and writing or numbers were made every thirty years at least. Now we innovate I-devices. All societies, even the mighty Rome, which by the way wrote the Bible (I personally am agonistic, so non-religious) crumble with time. Look around our economy's failing and the politicians and the 1% are forming an aristocracy, such a move from democracy to aristocracy was Rome's downfall. What proof do we have that our great empire won't fall? Especially with our pollution and corrupt leaders. (though in my opinion Obama is an awesome president.
Many great civilizations did not end in a crash, but, instead, just gradually declined in influence, while remaining stable and viable. Great Britain once ruled half the world, but even though it is no longer so powerful, it is still a perfectly functional country. Even the Roman Empire, which is often seen as the epitome of such a civilization, lasted in the East, as the Byzantine Empire, for another thousand years, after its fall. The U.S. is likely to decline in relative influence, but I see no reason, at present, to assume it will crash and burn.
While other great civilizations have come crashing down before, the U.S. will not. The government will not let things get so bad that they are beyond control. While the economy is in pretty tough shape, some people are still doing just fine. Once people start spending again, things will get better.
I think the fact that the United states has the system of checks and balances as well as the nearly perfect system of voting, so that it makes it more difficult for the country to ever come crashing down. There is plenty to prevent this from happening due to our government.