Staying out of World War I helped President Woodrow Wilson narrowly win re-election in November 1916. But five months later he summoned the country to battle against the German Empire with these words: “The world must be made safe for democracy. … We have no selfish ends to serve. We desire no conquest, no dominion.”

Now, 100 years later, the United States is recalling its pivotal role in the war that had turned Europe into a slaughterhouse and only ended after the Americans joined the fight.

Soldiers marching through destroyed town (© AP Images)
Troops from the 18th Infantry, First Division, amid ruins in a French town near St. Mihiel in July 1918 (© AP Images)

It began in 1914 after a young anarchist assassinated Archduke Franz Ferdinand of Austria. German forces occupied Belgium and parts of France, anticipating quick victory. But fighting dragged on and spilled over to other parts of the world.

Despite sympathies with Great Britain, France and their allies, the United States stayed neutral in the first years of the war. Commercial ties with the Allies remained strong, with the British navy controlling the seas — blocking Germany from accessing vital goods. Germany tried to break the Allied naval blockage with U-boats — submarines — that sunk military, merchant and civilian vessels, including the Cunard liner Lusitania in 1915. Among the 1,198 passengers killed were 128 Americans.

Vintage poster showing sailor and allegorical female figure (Library of Congress)
A U.S. Navy poster with a symbolic Liberty figure sending a sailor off to fight (Library of Congress)

The final straws were Germany’s resumption of unrestricted submarine warfare and the interception of the Zimmerman Telegram. The telegram revealed a German plot to help Mexico regain Texas, New Mexico and Arizona if it attacked America.

When the United States entered the war in April 1917, the U.S. Army had only 130,000 troops, no tanks and few planes. Congress quickly approved conscription to strengthen the forces. A German admiral scoffed that not many American fighters would reach Europe, with U-boats blocking their way.

But they made it. “Lafayette, we are here,” a colonel declared at the Paris tomb of the French nobleman who aided the American Revolution.

Lasting impact

The Allies were battered and depleted from over three years of trench warfare. The Americans played a significant role in the war’s last year, especially when German forces launched their final offensive. The arrival of the “doughboys,” as members of the American Expeditionary Force were sometimes called, helped firm up Allied lines and break German morale in the war’s waning months.

Four million Americans served in the military, 2 million were shipped to Europe, and 1.4 million engaged in combat, helping turn back the Germans at the Marne and fighting storied battles at Cantigny, Château-Thierry, Belleau Wood and St. Mihiel.

Sergeant Alvin York, initially a conscientious objector, entered military lore for charging a machine-gun nest in the Argonne Forest and killing or capturing more than 125 men.

Soldiers climbing over defensive sandbag wall (© AP Images)
American troops in France in 1918 (© AP Images)

“World War I forever altered America’s character,” writes Wilson biographer Scott Berg in World War I and America: Told by the Americans Who Lived It. “After supplying humanitarian relief to faraway countries during the early part of the war, the United States proceeded to act further on a moral imperative, offering the commitment of the entire nation in the name of peace and freedom.”

Vintage photo of women working in factory (© AP Images)
Women operating drill presses to make railcar motors in 1918. As men went off to fight, women took their places in factories vital to the war effort. (© AP Images)

The war confirmed the United States as a leading player in international affairs. At home, it expanded the size and reach of government and even helped women secure the vote after thousands joined the military and toiled in factories. African-American troops fought valiantly in France, then began a decades-long struggle against segregation at home.

Soldier carrying backpack (Library of Congress/Lewis Hine)
A “doughboy,” a nickname for members of the American Expeditionary Force, arrives in Paris. (Library of Congress/Lewis Hine)
Poster showing hand about to pitch ball labeled "Second Liberty Loan of 1917" to Kaiser Wilhelm, who holds bloody sword as bat (Library of Congress)
A Liberty Bond poster. Twenty million people purchased $17 billion in interest-bearing bonds for the war effort. (Library of Congress)

Patriotic fever swept the country, captured in the stirring George M. Cohan anthem “Over There,” Liberty Bond drives, and posters urging men to enlist and everyone to conserve food.

The Ultimate Sacrifice

By Nov. 11, 1918 — Armistice Day — 9 million soldiers and 5 million civilians lay dead, slain not only in battle but by epidemics and starvation.

Troops marching through city, spectators watching (© AP Images)
Victorious soldiers paraded past the Flatiron Building and Madison Square in New York City after returning home in 1918. (© AP Images)

While the U.S. sacrifice did not match those of the other major combatants, the nation suffered 116,516 military deaths, including Lieutenant Quentin Roosevelt, youngest son of former President Theodore Roosevelt, shot down over France.

Cities and villages across Europe and in the United States erected memorials to their dead. At Arlington National Cemetery on November 11, 1921, President Warren Harding dedicated the Tomb of the Unknown Soldier containing a doughboy’s remains. “We know not whence he came, but only that his death marks him with the everlasting glory of an American dying for his country,” Harding said.