Traveling from across the world to battlefields where their soldiers fell 100 years ago, victors and vanquished alike celebrated those sacrifices ahead of Sunday's Armistice Day and assessed a future in which it is increasingly difficult to see where the United States stands.

A century ago, the entry of U.S. troops into World War I tipped the momentum toward its allies, including France and Britain. On Saturday, as he began two days of remembrance of the 1914-18 war, U.S. President Donald Trump said his nation bears far too much of the burden to defend the West.

In a flurry of armistice diplomacy, Trump and French counterpart Emmanuel Macron displayed an awkward coolness during their bilateral meeting, at odds with the chummy warmth that had marked former meetings between the two.

The nationalist and protectionist Trump has increasingly clashed with European allies over his America-first policies, and he was true to form during his trip to Paris, shooting off an angry tweet saying Macron's views on European defense are "very insulting."

At their meeting early Saturday, Macron seemed eager to keep up a show of camaraderie, and asked about the tweet, he reached out to pat Trump on the thigh. Trump was cordial - but sat stone-faced during the thigh tap.

There were fewer efforts at cordiality with Germany, which Trump singled out for criticism during an ill-tempered NATO summit over the summer. Though both were in Paris for the ceremonies, German Chancellor Angela Merkel and Trump had no meetings scheduled.

Instead, Merkel was marking how her nation's bloodstained history with France has become a close alliance that is now the driving force behind the European Union. She and Macron will together visit the site where the armistice was signed in a railway carriage in Compiegne, north of Paris.

In four years of fighting, remembered for brutal trench warfare and the first use of gas, France, the British empire, Russia and the United States had the main armies opposing a German-led coalition that also included the Austro-Hungarian and Ottoman empires.

Almost 10 million soldiers died. France lost 1.4 million and Germany 2 million.

Yet, despite a war that was supposed to end all wars, World War II pitted both sides against each other once again.

Across the line that once marked the Western Front, leaders lauded the courage of soldiers who were killed during the unprecedented slaughter before converging on Paris for a dinner.

That armistice entered into force on the 11th hour of the 11th day of the 11th month of 1918, and on Sunday 69 world leaders will mark the centennial of the event at the Tomb of the Unknown Soldier, underneath the Arc de Triomphe in central Paris.

At dawn Saturday, Canadian Prime Minister Justin Trudeau went to Vimy Ridge, the battlefield in northern France where Canada found its sense of self when it defeated German opposition against the odds.

Standing amid the white headstones against an ashen sky, Trudeau addressed the fallen, saying what Canada has achieved in the past century has been "a history built on your sacrifice. You stand for the values on which Canada was built."

In southern Belgium's Mons, Canadians were also lauding George Price, the last Commonwealth soldier to die in the war when he was shot by a German sniper two minutes before the armistice took effect.

Trump was looking beyond the tragedy of death and destruction, asking in a tweet: "Is there anything better to celebrate than the end of a war, in particular that one, which was one of the bloodiest and worst of all time?"

After his meeting with Macron, Trump was scheduled to head to the battlefield of Belleau Wood, 90 kilometers (55 miles) northeast of the capital, where U.S. troops had their breakthrough battle by stopping a German push for Paris shortly after entering the war in 1917.

The battle of Belleau Wood proved America's mettle to allies and foes alike, and by the time the war ended U.S. forces were at least an equal to any of the other major armies, which were exhausted and depleted.

However, Trump canceled his visit because of bad weather.