From a fascinating series over on Slate:
Hurricane Katrina proved that modern America is resilient. It didn’t prove that we’ll be around forever. After watching the place where I grew up avert total annihilation, I can’t help but wonder what course of events will eventually wipe out New Orleans and America as a whole. When it comes to human civilization, entropy conquers all: Rome fell, the Aztecs were conquered, the British Empire withered, and the Soviet Union cracked apart. America may be exceptional, but it’s not supernatural. Our noble experiment, like every other before it, has to end sometime.
The pessimists among us could be excused for thinking the country will run aground tomorrow. The U.S. military is understaffed and overstretched, global warming threatens to Atlantis-ize our coastal cities, and the strongest fundamental of our economy is that we need China to keep lending us money. General Motors—once an indomitable symbol of American might and ingenuity—filed for bankruptcy, and Glenn Beck, Fox News’ ascendant superstar, makes ratings hay by forecasting the apocalypse, American-style. Russian political scientist Igor Panarin has even predicted that the United States will break apart in 2010.
Be sure to read the various thought experiments of how the US could end!