Paris: At a weekend commemoration of the 100th anniversary of the end of World War I, the president who proudly declares himself a “nationalist” stood apart, even on a continent where his brand of populism is on the rise.

He began his visit with a tweet slamming the French president’s call for a European defence force, arrived at events alone and spent much of his trip out of sight in the American ambassadors’ residence in central Paris.

On Sunday, he listened as he was lectured on the dangers of nationalist isolation, and then he headed home just as the inaugural Paris Peace Summit was getting underway.

The visit made clear that nearly two years after taking office, Trump has dramatically upended decades of American foreign policy posture, shaking allies. That includes French President Emmanuel Macron, who on Sunday warned that the “ancient demons” that caused World War I and millions of deaths were once again making headway.

Macron, who has been urging a re-embrace of multinational organizations and cooperation that have been shunned by Trump, delivered a barely veiled rebuke of Trumpism at the weekend’s centerpiece event: A gathering of dozens of leaders at the Tomb of the Unknown Soldier at the base of the Arc de Triomphe to mark the passage of a century since the guns fell silent in a global war that killed millions.

“Patriotism is the exact opposite of nationalism: Nationalism is a betrayal of patriotism,” Macron said, adding that, when nations put their interests first and decide “who cares about the others” they “erase the most precious thing a nation can have … its moral values.”

After Trump was gone, German Chancellor Angela Merkel, who recently announced that she will not be seeking re-election, made an impassioned plea for global cooperation at the peace forum, saying World War I had “made clear what disastrous consequences a lack of compromise in politics and diplomacy can have.”

Trump, who has made clear that he has limited patience for broad, multilateral agreements, sat mostly stone-faced as he listened to Macron, who sees himself as Europe’s foil to the rising nationalist sentiment, which has taken hold in Hungary and Poland among other countries.

Also travelling on his own was Russian President Vladimir Putin, who shook Trump’s hand, flashed him a thumbs-up sign and patted Trump’s arm as he arrived. Trump responded with a wide smile.

National security adviser John Bolton had said at one point that Putin and Trump would meet in Paris, but they will instead hold a formal sit-down later this month at a world leaders’ summit in Buenos Aires.

Trump, who ran on an “America First” platform, has jarred European allies with his actions.

Trump has slapped tariffs on the European Union, pulled the US out of the landmark Paris Climate Accord and the Iran nuclear deal and suggested he might be willing to pull the US out of NATO if member counties don’t significantly boost their defence spending.

Trump’s eagerness to get along with the Russian leader in spite of Russia’s meddling in the 2016 election and numerous other aggressive moves in recent years has alarmed those who view Russia as a growing threat.