One of the assumptions that economists sometimes use to frame their models is to specify that some variables will be held constant, a concept that’s expressed with the Latin phrase “ceteris paribus.”

We often make the same mistake in politics and foreign policy. We concentrate on our own domestic issues and assume that the rest of the world will remain fixed while we sort them out. We’ll get back to you later, in 2021, say.

But the world moves on. It’s dynamic, not static: Erratic changes in one country produce reactions in other countries; alliances that once seemed solid become weaker and are recast; ambitious powers exploit new opportunities created by shifting dynamics; some countries rise, and others fall.

Last weekend’s events in Paris offered a dramatic demonstration that “other things being equal” is not a safe assumption. The world is moving to adapt to the reality that Donald Trump is president of the United States. Our friends and allies may hope his election eventually will be reversed, and maybe they think America turned a corner with the 2018 midterm elections. But they can’t count on it, so these countries must consider that America may be a different country from what they had believed.

French President Emmanuel Macron articulated this reality last week. In one of his World War I remembrances, he told a French radio station that Europe needs a “true European army” at a time when America is a less-reliable ally. “We have to protect ourselves with respect to China, Russia and even the United States of America,” Macron said.

Trump blasted Macron’s comments as “very insulting,” and he continued to complain in tweets Tuesday about French ingratitude and claimed Macron was trying to distract from his “very low” approval ratings. But joining Macron on Tuesday was German Chancellor Angela Merkel, who told the European parliament that she shared others’ view that “a common European army would show the world that there would never again be war in Europe.”

Trump set the NATO alliance wobbling from the day he took office, raising doubts about America’s continued readiness to pay for other countries’ defense. Europeans spent a year trying to make nice, but they seem to have gotten the message. American isn’t a fully reliable protector anymore. Europeans do indeed have to take greater responsibility for their defense -- and depend less on a US-led NATO. What Trump has done is folly, in my view, but it’s precisely what he wanted.

The world is moving on, in other ways, from Trump’s “America First” idea of US power. Macron announced Monday the “Paris Call for Trust and Security in Cyberspace.” The document proposed a basic code of conduct to prevent meddling in elections and other malicious hacking. It was backed by more than 50 countries, 90 nonprofits and 130 private companies, including Microsoft, Google, Facebook and IBM. Absent from the list was the US -- along with Russia, China, Iran and Israel. Nice: The big five of cyberwar.

But the “Paris Call” alliance of countries, corporations and NGOs will probably move forward on cyberspace -- just as a similar global coalition has remained intact to fight climate change, despite the Trump administration’s refusal to participate.

As Trump’s America retreats from global diplomatic engagements, other opportunistic countries are stepping forward. The most obvious example is Russia. President Vladimir Putin may hold a weak hand, but he’s in the game. Russia talks with everyone: Israel and Iran, Saudi Arabia and Turkey, the Taliban and the Afghan government. Putin may be a bullyboy, but he’s wearing a diplomat’s striped pants -- sponsoring negotiations on Syria, Afghanistan and other issues. Once upon a time, America owned this role of global broker, but not anymore.

The greatest beneficiary of Trump’s retreat is China, which openly proclaims its desire to challenge US global primacy. A senior Australian official told me this week that everywhere Australia looks in Asia, it sees China seeking to find potential bases for its increasingly powerful military. Australia is one of the countries that has relied upon American power, and officials still hope that’s a good bet. But looking at Trump, they have to wonder.

Commentators have noted that 1918 marked a global inflection point. After the horror of World War I, empires collapsed, aristocracies faded, aggrieved citizens challenged and eventually toppled the old order. Another transitional year was 1945, which began a half-century of overwhelming American global dominance.

America suffered a political hiccup in 2016, electing a man who was manifestly unprepared to be president. Most of the world hopes we’ll find our balance again, but in the meantime, they must consider making other arrangements.


David Ignatius
David Ignatius’ email address is davidignatius@washpost.com. -- Ed.

(Washington Post Writers Group)