In London, Prince Charles laid the first wreath of red poppies, Britain's emblem of remembrance, at the nation's annual commemoration ceremony on behalf of his mother Queen Elizabeth II, who watched from a nearby balcony.
Russian President Vladimir Putin is expected to attend the lunch following the ceremony, and Trump has said that if the two meet during their time here it would likely be for just a brief interaction at the palace.
The "America First" leader, who faced criticism on Saturday for cancelling a trip to an American cemetery because of rainy weather, will snub the Peace Forum.
President Trump tweeted back: "President Macron of France has just suggested that Europe build its own military in order to protect itself from the U.S., China and Russian Federation". The feminist activist group Femen later claimed responsibility.
In response to Zakaria's question about Trump's tweet being a mistake, Macron said, "I always prefer having direct discussion or answering questions (than) making my diplomacy through tweets".
Macron said "nationalism is a betrayal of patriotism".
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.
The President took to Twitter within moments of his touchdown in Paris to say that the French leader's plan for a European military was "insulting".
In Paris, German Chancellor Angela Merkel was due to give the opening address alongside UN Secretary General Antonio Guterres at a peace conference following the memorial service on the Champs-Elysees.
In his remarks at the cemetery, Trump said, "The American and French patriots of World War I embody the timeless virtues of our two republics".
Mr Peters said it was a humbling experience to be there.
An American delegation led by Chief of Staff General John Kelly and Chairman of the Joint Chiefs of Staff Joe Dunford did visit the Aisne-Marne American Cemetery and Memorial under gray skies and drizzle, paying respect to the almost 2,300 war dead buried there. You know what I am?
Do we govern ourselves as sovereign nation-states and sovereign citizens or as interdependent global communities of world citizens?
"The aim of the forum is to show that there are lots of forces in the worldwide system - states, NGOs, foundations, intellectuals, companies - who believe we need a world of rules, an open world and a multilateral world", chief organiser Justin Vaisse told AFP.
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.
Trump delivered the speech as other leaders were gathered for the Paris Peace Forum, which aims to revive collective governance and worldwide cooperation to tackle global challenges.
Trudeau sat beside Putin and the pair briefly chatted at the opening session of Macron's peace summit on Sunday. Its role as host of the main global commemoration aimed to highlight the message that the world must not stumble into war again, as it did so quickly and catastrophically with the second world war.