After a lunch with Macron and their wives, Melania and Brigitte, Trump was scheduled to visit an American cemetery at Belleau Wood, east of Paris. The two men are meeting in Paris on Saturday, and Macron's office says this issue will be on the table.
The decision prompted a rash of criticism on Twitter, with Nicholas Soames, a British member of parliament who is a grandson of former Prime Minister Winston Churchill, saying that Trump was dishonoring US servicemen.
"We are going to a very important ceremony marking the centenary of the end of World War I. This was A bloody war that claimed millions of lives", he said at the airport before his departure.
He first lady Melania Trump skipped an arrival ceremony at the residence of the French president earlier in the day and did not walk down the Champs-Elysees with other world leaders, traveling to the Arc de Triomphe in the US president's bullet-proof limousine, instead.
Some 10,000 police have been drafted in to ensure maximum security in a city repeatedly targeted by terrorists.
On Saturday evening, they will join other world leaders for a dinner hosted by the Macrons at the Musee d'Orsay museum, ahead of Sunday's armistice commemorations at the Arc de Triomphe, where the Unknown Soldier is buried. Macron and Merkel unveiled a commemorative plaque where the Armistice was signed, ending the war.
The memorial is doubly symbolic as Adolf Hitler forced the French to return to it on June 22, 1940 to sign their own surrender at the start of World War II.
President Emmanuel Macron and German Chancellor Angela Merkel used the occasion Saturday to laud European peace and to demonstrate, in person, how countries that were once bitter enemies need not stay that way.
Populism and nationalism are gaining in popularity, while countries are putting up barriers against globalization, she said.
"I think he has shed any illusion about Trump that flattering him will be a way of getting concessions", said Thomas Wright, a Europe expert at the Brookings Institution.
Trump is not expected to attend the Peace Forum.
In Paris, the jewel that Germany sought to capture in 1914 but which the Allies fought successfully to defend, the armistice commemorations were being followed by the afternoon opening of a peace forum pushed by the host, French President Emmanuel Macron.
"We want a strong Europe, it's very important to us, and whichever way we can do it the best and more efficient would be something we both want", said Trump.
Discussing the growing dangers from cyber-hacking, meddling in electoral processes and the U.S. decision to withdraw from a missile treaty, Macron said Europe needed to protect itself against China, Russia "and even the United States".
"We will not protect the Europeans unless we decide to have a real European army", Macron said, emphasizing Europe needs an army to reduce dependence on the U.S.
"We have to protect ourselves with respect to China, Russia and even the United States".
Both leaders agree there should be "better burden-sharing within NATO", meaning Europe should be less reliant on USA spending for its defence, Macron said.
At Saturday morning's meeting, they were able to agree on "burden sharing" for North Atlantic Treaty Organisation countries. That's why I do believe that we need more European defence in order to take this part of the burden.