The commentariat is bursting with speeches, diatribes, essays, analyses, stories and tweets about the impending collapse of the post-World War II international order. This threatens global peace and prosperity, even if we’re not entirely sure how the threat might actually materialize.

When we say “the post-World War II international order,” we mean a series of political, military and economic alliances whose members pursue common goals and embrace common values. Led by the United States, the system arose during and after the war mainly as a counterpoint to the Soviet Union. Countries believed that their narrow national interests were served by advancing a collective agenda.

It is this system — a state of mind as much as a set of formal obligations — that is now coming apart, reeling from President Trump’s frontal assault on its premises. But, although Trump is the immediate cause of the present turmoil, he is not the only cause. Let’s examine the larger context.

Start with Trump, because his role is the easiest to understand. By any conventional standard, he is acting irrationally and erratically; worse, he’s supported policies that harm the United States. He is deliberately starting a trade war that could derail the global economy. He not only disagrees with our traditional allies (Europe, Japan, Mexico, Canada), but he has gone out of his way to insult them. Even if the leaders of these countries were willing to let bygones be bygones, their citizens may not be so tolerant. Public opinion will make cooperation with the United States harder.

But ordinary rules of logic do not apply to Trump. Almost everything he has done can be explained by personal ambition. He is not interested in policy, nor in making America great again. (America was greatest in and after World War II, precisely when it was doing the most for other countries.) The president’s all-consuming passion is to make Donald Trump great.

He needs to be the center of attention — not just sometimes but all the time. The more outrageous, offensive, unexpected and egotistical something is, the more he likes it because it thrusts him onto center stage, where he wants to be. That’s his policy. There is great consistency in his behavior, even if some of his actions repudiate what he has said or done earlier. (Not surprisingly, Trump’s meeting with North Korean leader Kim Jong Un is a reprise of America’s role as global leader.)

Granted, not everything that is wrong with America’s relations with its “allies” — or, for that matter, their relations with us — can be blamed on Trump. If matters were so simple, we could outwait or outwit him. The reality is more complicated. The passage of time has weakened or destroyed the lesson that the World War II generation took from the war: Two decades of isolationism after World War I had not shielded us from the greatest calamity in human history. Because isolationism didn’t work, Americans were in no mood to try it again (especially with a nuclear-armed Soviet Union). This shift in public opinion served as a crucial backstop to an outward-looking foreign policy.

But the World War II generation — the people who experienced this political and emotional conversion — is mostly dead, and younger generations are of a different mind. Baby boomers lived in the shadow of World War II and absorbed some of its lessons; but many also concluded that, in Vietnam, the country had taken the lessons too far. Later generations have been even less imbued with the value of America’s global role.

The point is that America’s leaders have not been able (some would say they didn’t try very hard) to create public support for a new internationalism, based on today’s realities. The 2008-09 global financial crisis further undermined public confidence.

Still, most of what we seek to achieve — including a stable global economy, relief from terrorism, protections against cyberattacks and consistent environmental goals — depends heavily on international cooperation. We were vulnerable to a Trump, whose simplistic nationalism sounds more appealing than it is.

Finally, our allies have not always been the best of allies — and we have not always been the best of leaders. Long before China joined the World Trade Organization in 2001, Japan and some other countries practiced mercantile policies of favoring select industries. Most members of NATO have underspent on their military, even though the official spending target (2 percent of gross domestic product) is modest. Similarly, the United States has periodically resorted to protectionist measures to defuse political opposition to imports.

It’s a bleak backdrop. Trumpism is leading to a global power vacuum. Who, if anyone, will fill it? China? Russia? No one?

Robert Samuelson is a columnist with The Washington Post Writers Group.