LONDON — Seconds before an armistice formally ended World War I on Nov. 11, 1918, Pvt. Henry Nicholas Gunther, an American soldier from Baltimore, mounted a final, one-man charge against a German machine-gun nest in northeastern France.

The German gunners, The Baltimore Sun reported many years later, had tried to wave him away, but he ran on, only to perish in a burst of heavy automatic fire — the last soldier of any nationality to die in the conflict — at 10.59 a.m. local time. One minute later, under the terms of an armistice signed about six hours earlier, the so-called Great War, the “war to end all wars,” was over, and the world was an altered place.

The casualties since the conflict’s first engagements in 1914 ran into many millions, both military and civilian. The very nature of warfare had changed irrevocably. Empires crumbled, new nations arose and the world’s maps were redrawn in ways that reverberate mightily a century later. With men away at the front lines, women assumed roles in the work force back home that hastened their emancipation and changed social ways forever.

The war’s unfolding had been punctuated by related events that would become markers in history: the Easter Rising in Ireland in 1916; the Russian Revolution a year later; the Sykes-Picot Agreement of 1916 and the Balfour Declaration of 1917, which together drew the parameters of the modern Middle East and foreshadowed the creation of Israel. In 1917, the United States entered the war with a decisive deployment of soldiers that was a first step toward taking on the status of a superpower.

[Explore our 2014 collection of stories marking the 100th anniversary of the outbreak of World War I, including maps, interactives and archive pieces.]

Against those overarching events, Private Gunther’s charge might seem no more than a postscript. Yet his “sad, senseless end,” as The Baltimore Sun put it, endures as an emblem of the courage and folly of a war that formally ended on the 11th hour of the 11th day of the 11th month in 1918. It is a reminder, too, of a different age of gallantry and pain, before human experience was compressed into a pixelated fragment, a fleeting distillate transacted on social media.

A century on, a question remains: Will, or should, this commemoration of Veterans Day — or Armistice Day, or Remembrance Day, as the date is also known — be the last on this scale? Should the world continue to pause in silence to honor the sacrifice and bravery of those who fought it on the ground — “lions led by donkeys,” according to a phrase used to scorn the bumbling British officer class drawn from the upper crust?

Some argue that commemorations have become no more than lip service. But the warnings against collective amnesia go back a long way. Even in 1915, long before the armistice, one of the most quoted poems of the war, by the Canadian military doctor Lt. Col. John McCrae, imagined fallen soldiers warning the survivors: “If ye break faith with us who die / We shall not sleep, though poppies grow / In Flanders fields.”

In today’s world of shifting international alignments, uneasy alliances and growing nationalism, World War I offers a reminder of how easily and unexpectedly an obscure spark can ignite a conflagration. In 2011, for instance, when the self-immolation of a fruit vendor in Tunisia helped start the Arab Spring, who would have imagined that, seven years later, his action could have built into crises that have spread across the region and rekindled rivalries reminiscent of the Cold War?

The 1914-18 war has found other curious, possibly inadvertent, echoes. At a campaign rally in Montana on Nov. 3, President Trump spoke about his efforts to prevent Central Americans from crossing the border into the United States, lauding what he called “all that beautiful barbed wire going up today.”

“Barbed wire, used properly, can be a beautiful sight,” he mused.

Barbed wire, which was invented in the 19th century, was long used to fence off cattle ranges in the American West. It figured, too, in the architecture of human incarceration. But in World War I, mile upon mile of coiled barbed wire wove through the blasted terrain of trench warfare to create entanglements that impeded foot soldiers and exposed them to withering fire and bombardment.

In 1918, in a poem titled “Exposure,” Wilfred Owen evoked the delusional nightmares of soldiers crouched in trenches, awaiting combat as a wintry wind howled over the battlefield. He, too, spoke of barbed wire, though not in terms of beauty. “Watching, we hear the mad gusts tugging on the wire, / Like twitching agonies of men among its brambles.” Owen died seven days before the Nov. 11 armistice stilled the guns.

[See pictures and read about how photographers braved the front lines to document the mass slaughter.]

The start of World War I is generally traced to events in Sarajevo, then a part of Austria-Hungary, on June 28, 1914, when Gavrilo Princip, a young Serbian nationalist, fired a handgun and assassinated Archduke Franz Ferdinand, the heir to the Hapsburg throne, and his wife, Sophie. The event caused a chain reaction that propelled alliances, ambitions and insecurities into a global conflict driven by technological advance — poison gas and battle tanks on land, combat planes in the skies, warships above the waves, and submarines below them.

A flurry of declarations of war and secret pacts in August 1914 drew the broad battle lines between, on one side, Germany, Austria-Hungary, the Ottoman Empire and their allies; and, on the other, Britain, France, Japan, Russia and their supporters. Over time, the fighting spread to faraway imperial outposts, including China, the Middle East and Africa. Often, the focus was on the stalemated battles of attrition that produced horrific casualties in Europe. On the first day of the Battle of the Somme in northern France on July 1, 1916, for instance, around 20,000 British soldiers died and some 40,000 others were wounded — casualties that set a gruesome benchmark in the annals of slaughter.

Campaigns on other fronts yielded some of the most humiliating defeats in British military history, such as the campaign on the Gallipoli Peninsula, in what is Turkey today, that began in 1915; and a siege that started later that year in Kut, south of Baghdad, in what is now Iraq.

According to the British historian Hew Strachan, by 1916, the old Napoleonic notion of wars ending with a decisive battle had given way to campaigns that “ended with a whimper, not a bang” and “proved more indecisive than decisive.”

When the Russian Revolution ended Moscow’s appetite for the war, Germany sensed victory. But then the United States entered the fray, with the first of its soldiers landing in France in June 1917. By 1918, big offensives on the Western Front had turned the tide. But not without punishing losses.

At the Meuse-Argonne American Cemetery in northeastern France, the largest American military graveyard in Europe, 14,246 white headstones mark the burial places of United States First Army soldiers who perished in the final, 47-day campaign that ended with the armistice.

It is worth noting that one of those headstones is that of Cpl. Freddie Stowers, the first black American to be awarded the Medal of Honor for his role in World War I as a member of a racially segregated unit. (It was awarded posthumously in 1991, more than 70 years after he was mortally wounded by machine-gun fire on Sept. 28, 1918.)

In light of America’s present-day passions over immigration, it is also worth observing that nearly a quarter of the draftees in 1918 were immigrants, the result of an influx that had transformed America’s demography into a “melting pot” of lineages — British, German, Hispanic, Italian, Slav — according to Geoffrey Wawro, a professor of history and director of the Military History Center at the University of North Texas.

Private Gunther was himself descended from German immigrants. His motives for his — literally — last-minute charge were unclear. According to some accounts, he had brooded over a demotion from sergeant after military censors intercepted a letter deemed to be critical of the conduct of the war. He “became obsessed with a determination to make good before his officers and fellow soldiers,” The Baltimore Sun reported. In one way, he may have succeeded: posthumously, his sergeant’s rank was restored, and he was awarded the Distinguished Service Cross.

The armistice was signed in a railroad car in the Compiègne Forest, north of Paris. It paved the way for the Treaty of Versailles in 1919, which imposed such onerous terms on the defeated Germany that it is often cited as a reason for Hitler’s Nazi ideology finding so much resonance. It was no coincidence that, when France fell to a vengeful Germany in 1940, Hitler chose the same railroad car, in the same location, for his French adversaries to accept their capitulation — as German commanders had done in 1918.