In a speech at the Suresnes military cemetery in the western Paris suburb, Trump paid tribute to U.S. soldiers who took part in World War I.
"Old demons are reawakening, ready to sow chaos and death", he said, warning of how ideology, religion and a disregard for facts could be exploited.
Nationalism is a betrayal of patriotism, ' he said in the American president's presence.
In a dinner late on November 10 with numerous visiting leaders, Macron warned against taking peace for granted. Trump and Putin arrived slightly later in separate motorcades. The move drew swift condemnation at home, as Republicans and Democrats alike cautioned Trump over the connotations of openly "nationalist" rhetoric.
A member of the British Parliament and grandson of legendary British Prime Minister Winston Churchill, Nicholas Soames, was even more critical, calling Trump "pathetic" and "inadequate" on Twitter because he "couldn't even defy the weather to pay his respects to The Fallen" who "died with their face to the foe".
After church bells rang out across France, the leaders sat together at the Tomb of the Unknown Soldier at the Arc de Triomphe for a memorial that included a performance by star cellist Yo-Yo Ma and the reading aloud of letters by WWI soldiers. White House press secretary Sarah Huckabee Sanders cited security protocols for the presidential motorcade's solo trip down the grand flag-lined avenue, which was closed to traffic.
"I want to speak of my concerns that are mixed in with today's commemoration, the concern that national blinders are spreading again, that actions are taken as if to simply ignore our mutual dependencies, relationships and binding ties", Merkel told the forum.
The U.S. president was also planning to skip the Peace Forum his host was organizing later on Sunday.
En route to the event, French police tackled two topless protesters who were sprinting toward the president's vehicle, "The Beast", but it was unclear whether the president and first lady were able to see them.
As he was arriving, a woman ran out toward the United States presidential motorcade with slogans - including the word "fake" - written on her chest.
Since then, the USA has sent National Security Adviser John Bolton for two rounds of talks with Russian officials, but the only deal announced publicly was a vague agreement for the two leaders to meet again next year, possibly in Washington.
Trump, who champions a nationalist "America first" policy, will not attend the forum but Putin is expected to.
"Each of these marble crosses and Stars of David marks the life of an American warrior-great, great warriors they are-who gave everything for family, country, God, and freedom", Trump said.
On the other side of the globe, Australia and New Zealand held ceremonies to recall how the war killed and wounded soldiers and civilians in unprecedented numbers and in gruesome new, mechanized ways.