Oooh, that sure is a provocative title. But this isn't about the 2004 election, terrorism, the rise of the right or left, or whatever. I'm thinking millennia. America is a young country, relatively speaking, being a bit under 230 years old. Even if you date America to the voyage of Columbus, we're just over 500 years old. Realistically, we've been a world power for a little under a century. 

The Romans were dominant for (ballpark) a millennium. The Egyptians maybe around the same. The Chinese dynasties, a few millennia. So it isn't unreasonable to think that America can be the dominant world power for somewhere between 1,000 and 3,000 years. We've got a long way to go, but sooner or later, America will no longer be the most important country economically and militarily, and the only question is when and how.

This is treading dangerously close to being Science Fiction, but that's OK, I used to write SF as a hobby. There are a number of different scenarios for how America's dominance could end:

The sun explodes. This is the extreme case of "America will always be dominant," and I include it just to prove that, no, someday it has to end. Five billion years, give or take a few, but we're all going to be starstuff once more.

America dies of obesity. Very gradually, and over time, the government gets more and more bloated, less and less efficient. Corruption becomes more common (say what you like, the United States is one of the least corrupt countries in the world), and it gets harder and harder to get anything done. Wealthy people find more ways to not pay taxes, which just forces rates higher for everyone else, and more of the economy goes underground. At some point, so little business is done through legitimate channels that the central government basically doesn't matter anymore, and people start spontaneously forming their own new governments.

The dandelion puff. Future efforts to colonize space are wildly successful, and the economic center of gravity gradually shifts to outer space. America may remain the dominant power on Earth, but the real power lies outside Earth's atmosphere. Living at the bottom of a deep gravity well is a huge military disadvantage, so there's not much question of who wins when push comes to shove. Earth becomes like "Old Europe," and America the equivalent of France or Germany: important, but no longer calling all the shots.

All Hail Bob! America's representative democracy becomes more and more dysfunctional, until power is seized by the equivalent of an American Emperor. This will be welcomed by most Americans, since it returns some rationality to the system; but to appease those who remember a golden age of Democracy, Congress will continue on as an increasingly less important body. This is the Roman model, but heaven help us if "Sharpton" ever becomes a title synonymous with "Emperor."

America as Precursor. Other regions become more united and more powerful, but adopt government and economic models more and more similar with America's. Gradually, a de-facto world government emerges, as barriers between regions drop and cooperation increases: think the European Union without Brussels. Eventually, a formal, elected President of the World may emerge, who will initially be either Indian or Chinese. America is viewed as the experiment which took over the entire petri dish.

Foreclosure. Government debt grows and grows until a fiscal crisis forces the government to either print huge numbers of dollars (thus making them worthless), or go bankrupt. Foreign creditors threaten to seize American assets overseas, which would effectively destroy nearly every large corporation in the country. As a compromise, Florida is given to China in exchange for debt forgiveness, and Disneyworld is allowed to become its own sovereign nation, thus posthumously fulfilling Walt Disney's lifelong dream. Thus weakened, America's economy never recovers enough to become overwhelmingly dominant again, though America remains one of several important countries.