America has long fancied itself to be a David — the plucky underdog that triumphs against all odds. But a David needs a Goliath, or the story doesn't work. And so America has looked for Goliaths to define itself against.
The Puritans saw themselves as a chosen people in a covenant with God — the same God who had demanded of the Israelites that they not be like other nations. They could only be "a city on the hill," an example to all those other nations, if they managed to succeed in not being like them. The idea of America as a new Israel would persist past the 17th century. Benjamin Franklin wanted the Great Seal of the United States to depict the Red Sea closing on Pharaoh and his chariots. There, of course, the Pharaoh represented the tyranny of the British. From the beginning of the new nation, American identity was wrapped up in opposing tyrants.
Later, in the era of mass European immigration in the late 19th century, America defined itself largely against Europe. "The New Colossus," the poem that greets immigrants from where it's engraved on the Statue of Liberty's pedestal, illustrates this attitude well. Hardly anything in it is about freedom, aside from the closing image of the golden door. Instead, it dwells on the contrast between the "storied pomp" of Europe's "ancient lands" and the sorry state of the inhabitants who are leaving it behind.
A similar dichotomy made an appearance during World War II and the Cold War. The idea of American identity primarily being about commitment to various ideas — liberalism, democracy, capitalism — emerges here because first America's enemies in World War II, and then the Soviet Union, defined themselves against them. Nikita Khrushchev claimed that "we will bury you," and many people thought he was right. Whittaker Chambers, a Soviet spy who eventually left the Soviet underground and became a fervent anti-communist, thought he was joining the losing side by doing so.
But now the Soviet Union is gone. Europe is almost entirely part of the American orbit. Nearly no one believes anymore that America is in some sort of covenant with God that sets it apart from every other nation. The United States is now the most powerful country in the world. In other words, it's Goliath.
It's harder to create a positive vision of what you stand for than it is to simply point elsewhere and say you're against that. As A. E. Housman, the classicist and poet, once observed, poets never write poems about liberty; instead, "they substitute images … and in the last resort, they fall back on denunciation of tyranny, an abominable institution, no doubt, but at any rate less featureless than Liberty, and a godsend to people who have to pretend to write about her."
It's also much easier to unify people when you have an opposing force you can rally against. Past American self-conceptions have always relied on the U.S. being a new idea, an experiment, an underdog. They break down when America is the global hegemon and when American culture and ways of thinking saturate almost everywhere.
The years since the fall of the Soviet Union have seen a lot of casting around for a new worthy adversary. Islamic terrorism, Saddam Hussein, North Korea, Iran, and Russia, among others, have all gotten their turn. None of it has worked, though, since the average American knows that the two sides here are not equal, or anything close to it.
Will China provide a solution to this identity crisis, as it were? I doubt it. The attempts to re-use the anti-Soviet playbook have the flavor of a cargo cult. Repeating the old lines won't make them true. The Chinese don't have an ideology that opposes what Americans hold dear — many Americans can't even describe what their ideology is. (It's definitely not Maoism, even if they say so.)
Certainly, the Chinese don't talk like the Soviets did about how the triumph of communism is inevitable, and America trades far more with China than it ever did with the Soviet Union. Even its cultural relationship with Beijing is different. China has been seen as a market to tap into for so long by established institutions of American culture — the NBA and Hollywood, to name just two — that pivoting to seeing them as the unequivocal enemy would take time.
But if America can't or won't define itself against China, there aren't any other options. Yet a Goliath can't act like a David. The Iranians can refer to America as the Great Satan, but imagining it the other way around is laughable. It's always amusing when athletes and teams talk about how "nobody believed in us" despite being favored to win. An individual athlete or a team can believe such a self-delusion, sure. But not a country of 330 million.
John Quincy Adams once warned a younger America not to go abroad "in search of monsters to destroy." But America has always used monsters abroad to create its sense of self-identity and availed itself of the tricks Housman mentioned. Now it has to define itself without them.