One insistent question that will shape 2017 is whether we’re witnessing the gradual decay of the post-World War II international order, dominated by the economic and military power of the United States.

After the Soviet Union’s collapse in 1991, it became fashionable to talk of the United States as the only true superpower. Pax Americana would promote peace and prosperity. Globalization and trade would bind countries together. The U.S. economic and political model, mixing markets and government oversight, would be emulated. Higher living standards would bolster democratic ideas and institutions.

As for raw military power, no country could challenge the United States. The 1990-1991 Gulf War seemed to prove this. Of course, there were fearsome nuclear weapons. But they seemed safely stalemated. Few countries had them, and the largest arsenals, the American and Russian, seemed neutered by a shared understanding that everyone would lose in a nuclear exchange. The stage was set for what one prominent commentator called “the end of history.”

It wasn’t. Obviously, this reassuring vision no longer describes the real world, if it ever did. On all fronts, the actual future confounds the imagined future.

Economies around the world have slowed. In virtually every major country — the United States, China, Germany — growth has declined from what it once was, creating a global slowdown. Not surprisingly, the supposed connection between greater prosperity and democratic politics failed to materialize.

(Sarah Parnass,Bastien Inzaurralde/The Washington Post)

Democratic disillusion has paralleled economic disappointment. Globalization and trade have fallen into disrepute, charged with reducing the wages and jobs of industrial workers in advanced societies. With aging populations, governments in these countries are overcommitted. They struggle to pay costly welfare benefits. Public opinion, rather than strengthening democratic ideals, has veered toward economic populism and nationalism. Hello Brexit and Donald Trump.

The notion of a sole surviving superpower has also fared poorly. Power is the ability to get (or take) what you want. By this standard, China and Russia rank as important powers. Indeed, the very term “superpower” may be misleading or obsolete. The United States cannot get everything it wants simply by dispatching troops to hot spots.

Finally, the nuclear consensus is fraying. North Korea has atomic weapons; Iran may someday get them. The more countries that have nuclear arms, the more likely that someone will make a catastrophic miscalculation.

After World War II, the United States stumbled upon a global strategy. It would protect its allies militarily while hoping that peace would promote prosperous, stable and democratic societies. Communism’s psychological and political appeal would be rejected. Despite many setbacks, the strategy generally succeeded. Europe and Japan rebuilt; the Soviet Union failed; communism was discredited.

It is this narrative that the United States sought to project onto the post-Cold War international order. What we did not anticipate was the reaction of other countries and the complexity of history.

The international order is now in a state of flux for many reasons. Starting with China and Russia, many countries resent the United States’ leadership role. Many Americans have also tired of it. New technologies (notably, e-commerce, cyberwarfare) are further redistributing power and influence.

What’s curious is that American leaders have sometimes contributed to the decline of U.S. power. Barack Obama’s disdain of military force is so deeply felt and visible that the use of the United States’ fighting capabilities was often discounted by allies and adversaries alike, as in Syria. This has consequences, as my colleague Richard Cohen has knowingly written:

“Since the end of World War II, American leadership has been essential to maintain world peace. Whether we liked it or not, we were the world’s policeman. There was no other cop on the beat. Now that leadership is gone. So, increasingly, will be peace.”

Trump has his own ideas about weakening the international order. His chosen field is trade. He threatens to slap stiff tariffs on U.S. imports from China and Mexico. If these ignite a trade war, the adverse side effects may well backfire on U.S. workers and firms. The last time mass protectionism was tried as economic stimulus was the 1930s; the experiment did not end well.

There is a larger issue here. In his latest book, “World Order,” Henry Kissinger argues that the world is at its greatest peril when the international order is moving from one system to another. “Restraints disappear, and the field is open to the most expansive claims and the most implacable actors,” he writes. “Chaos follows until a new system of order is established.” It’s a sobering warning.

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