Mark Steyn has a piece in the New Criterion laying out the case for American (and British) decline:
According to the cbo's 2010 long-term budget outlook, by 2020 the U.S. government will be paying between 15 and 20 percent of its revenues in debt interest—whereas defense spending will be down to between 14 and 16 percent. America will be spending more on debt interest than China, Britain, France, Russia, Japan, Germany, Saudi Arabia, India, Italy, South Korea, Brazil, Canada, Australia, Spain, Turkey, and Israel spend on their militaries combined. The superpower will have advanced from a nation of aircraft carriers to a nation of debt carriers.....
Within the next five years, the People's Liberation Army, which is the largest employer on the planet, bigger even than the U.S. Department of Community-Organizer Grant Applications, will be entirely funded by U.S. taxpayers. When they take Taiwan, suburban families in Connecticut and small businesses in Idaho will have paid for it. The existential questions for America loom now, not decades hence. What we face is not merely the decline and fall of a powerful nation but the collapse of the highly specific cultural tradition that built the modern world.
I don't share Mr. Steyn's pessimism, but no one writes the declinist case better, or funnier, that Mr. Steyn.