Over Britanny lobster and Bresse chicken, Trump, Putin, Macron and Gutteres, sitting next to each other, were able to have a "rich, free-flowing discussion" about hot issues such as Iran, Syria, Saudi Arabia and North Korea, the Elysee said. "The whole world owes this moment of real joy to the heroes who are not here to help enjoy it". The feminist activist group Femen later claimed responsibility.
Ahead of the ceremony, dozens of world leaders dressed in black strode shoulder-to-shoulder along the Champs Elysees toward the Arc.
A handful of senior administration officials, including White House Chief of Staff John Kelly, went in the president's place, while Trump remained behind at the ambassador's residence with no alternate schedule for hours.
Merkel very freely explained she is the German Chancellor. Its role as host of the main global commemoration highlighted the point that the world mustn't stumble into war again, as it did so quickly and catastrophically with World War II.
British Prime Minister Theresa May and Prince Charles attended a separate remembrance event in London, where thousands of well-wishers also paid their respects to fallen soldiers.
The Paris Peace Forum aims at promoting concrete actions toward peace and should be repeated every year, he said.
Donald and Melania Trump attend WWI commemoration after other world leaders
Macron said that the meeting of 84 world leaders at a ceremony in Paris to commemorate the armistice is a historic moment. She had slogans, included the words "Fake" and "Peace", written on her chest.
Between five and 10 million civilians are estimated to have been killed. Thank you to every leader and guest who came to Paris from all over the world this weekend to build peace.
"Ruining this hope with a fascination for isolation, violence or domination would be a mistake for which future generations would rightly find us responsible", President Macron told them.
While praising France for "a wonderful two days", Trump described his rainy stop at the American cemetery at Suresnes as "the highlight of the trip".
"They were starting to learn German in Paris before the United States came along", Trump said. Nearly 10 million soldiers died, sometimes tens of thousands on a single day. It has also inspired debate about underlying fears of Europe's dependence on the US for security.
While France has long borne shame for coming under German occupation during World War II, the French fought an extremely dedicated fight in World War I.
Referring to the Nazi occupation of southern France during World War 2, Mr Trump argued France should remember what the USA did to defend Mr Macron's country rather than branding it as a threat.
"More European efforts on defence is great but it should never undermine the strength of the transatlantic bond", said Stoltenberg at a forum in Berlin on Monday. It was a Serb teenager, Gavrilo Princip, who assassinated the Austro-Hungarian crown prince in Sarajevo in 1914 to set off events which led to the outbreak of war.