The American Century was the 20th, and we’re no longer there.

Things were bound to go downhill.

Like fourth-century Romans and post-World War II Europeans, Americans are beginning to realize they are no longer citizens of an unrivaled superpower. And they’re kind of freaking out about it.

Using a novel “purchasing power parity” measure, the World Bank estimates that China’s economy will surpass the United States later this year. By per-capita GDP – and most useful indices – the U.S. still maintains its lead. Nevertheless, many Americans agree with the thesis of Thomas Piketty’s book, Capital in the Twenty-First Century, that America’s boom days are behind us, unlikely to be seen again.

We compare where we are now with where we were 10, 20, 30 years ago, and where our parents were. Psychologically, if not fiscally, you’re better off never having experienced prosperity than to have had it and lost it. Downward mobility as America’s middle class has experienced it over the last 40 or 50 years – a boom-and-bust cycle featuring shorter expansions and longer, deeper recessions and depressions – is a bummer.

“We’re walking small,” New York Times columnist Frank Bruni wrote on May 3. “And that shift in our gait and our gumption has been palpable for many years, during an unusually sustained period of frustration that has the feel of something more than a temporary dive: a turned corner, the downward arc of a diminished enterprise.”

As Bruni points out, we have good cause for bad ennui: America’s shameful global ranking on education quality (No. 39), collapsing social mobility (it’s easier to get rich in Old Europe and Canada), and our crumbling infrastructure. China unveils its awesomely cool-pressurized bullet train to the Tibetan plateau; our Amtraks, when they’re not hours late, derail.

Not that the U.S. doesn’t have at least as much money as it used to. Overall, the U.S. is richer. The trouble is, all our loot has gotten aggregated into the claws of too few people. As the Times’ Nicholas Kristof notes, “Overall, the United States’ economy outperformed France’s between 1975 and 2006. But 99 percent of the French population actually enjoyed more gains in that period than 99 percent of the American population. Exclude the top 1 percent, and the average French citizen did better than the average American.”

Of course, Americans have always worried that America was in decline. “A kind of depression has set in,” Washington Post columnist Richard Cohen wrote in 2011. “We’ve lost our mojo, our groove.”

Jimmy Carter’s 1979 “malaise” speech (which, despite our faulty collective memory, contains neither the word “malaise” nor “ennui”) addressed a “crisis of confidence the growing doubt about the meaning of our own lives and in the loss of a unity of purpose for our nation.”

Context matters, and it’s smart not to panic. Unless we really are screwed now.

In other words, it is entirely possible the events journalist James Fallows (who addressed the “we’re screwed” vibe in 2010) downplayed – environmental degradation; the military disasters in Vietnam, Iraq and Afghanistan; soaring energy prices and institutionalized political corruption – really were as bad as the worrywarts fretted because, throughout the conscious life of someone Fallows’ age, the U.S. really has been in decline.

The simple truth is that there’s only one world, and the U.S. is being forced to share its stuff. Despite a foreign policy centered around harassment of emerging major regional powers such as China, India, Brazil and Iran, Americans had better get used to a smaller share of power and wealth.

Which isn’t the worst thing. It sucked at the time, but losing their colonial empires is the best thing that ever happened to Europe’s once-great powers.

The question for Americans is: What do we do about it? Do we allow our slide into Third Worldism to continue? Or do we scale back the drones and stupid wars, reject the NSA’s Orwellian security nightmare, tax the hell out of the rich and rebuild the social safety net?

Ted Rall’s most recent book is The Book of Obama: How We Went From Hope and Change to the Age of Revolt.