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 under way.

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 organisations 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.

Bells tolled across Europe's Western Front and fighter jets passed overhead to mark the exact moment the devastating war came to a close.

With Trump and other leaders looking on, Macron took on the rising tide of populism in the United States and Europe and urged leaders not to turn their backs by turning inward.

"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.

Trump did engage with his fellow leaders, attending a group welcome dinner hosted by Macron at the Musee d'Orsay on Saturday night and a lunch on Sunday.

He also spent time with Macron on Saturday, when the two stressed their shared desire for more burden-sharing during a quick availability with reporters.

But Trump was terse during some of his private conversations with world leaders, according to people with direct knowledge of his visit. One of the people described the president as "grumpy."

The symbolism during Trump's visit couldn't have been more stark.

Trump was missing from one of the weekend's most powerful images: A line of world leaders, walking shoulder to-shoulder in a somber, rain-soaked procession as the bells marking the exact moment that fighting ended - 11 am on November 11, 1918 - finished tolling.

The president and first lady Melania Trump had travelled to the commemoration separately - White House press secretary Sarah Huckabee Sanders cited security protocols - from the other dignitaries, who had travelled together by bus from the Elysee Palace.

As Trump's motorcade was making its solo trip down the grand Champs-Elysees, which was closed to traffic, at least one topless woman breached tight security, running into the street and shouting "fake peace maker" as the cars passed. She had slogans, including the words "Fake" and "Peace," written on her chest.

Police tackled the woman and the motorcade continued uninterrupted. The feminist activist group Femen later claimed responsibility.

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.

Australian Associated Press