World War I was a watershed moment for America, a time when an isolationist nation involved itself in world affairs and began the rise to the economic and military power that America is today. After keeping out of the conflict that had been ravaging Europe for nearly three years, President Woodrow Wilson took America to war only months after winning an election on the slogan "He Kept us Out of War." Claiming that American intervention was needed to "make the world safe for democracy," Wilson sent over two million men to Europe, of whom over 100,000 would never return. World War I marked the end of the old order in Europe, and the beginning of what has been called the "American Century."
The United States was not a nation ready for war in 1914. With a small army and a pitiful navy, the U.S. was no match for either side in the great conflagration in Flanders' Fields. As the war continued, however, German use of submarines to sink neutral shipping—including, most famously, the sinking of the Lusitania in 1915 with the death of almost 1,200 people, 128 of them Americans—brought American public opinion to the Allied side. Constant British propaganda efforts, culminating in the Zimmermann Telegram of February 1917, coupled with the German resumption of unrestricted submarine warfare and drew America into the war. Wilson quickly developed an ideological goal of freedom and democracy, and committed the people of the United States to fight for these principles.
When America entered the war in April 1917, nearly three years of horrific slaughter had bled white the nations of Europe. Daily life in miserable trenches drove men insane; constant artillery bombardment killed without warning; massive infantry assaults through No Man's Land into barbed wire and machine guns caused the death of millions. New technologies including the machine gun, tank, airplanes, and barbed wire helped make the war the bloodiest the world had ever seen. As American soldiers landed in French ports by the thousands, the exhausted Allies screamed for the American units to be broken up and fed into the French and British lines under the command of French and British officers. General John Pershing, commander of the American Expeditionary Force, refused, insisting that the Americans fight together in their own section of the trench line under American commanders. This rift within the Allied high command almost cost the Allies the war during the German Spring Offensive of 1918, but Pershing's insistence that American soldiers fight under American commanders sent an important message of American independence to the world.
American soldiers fought bravely and well in battles at Cantigny, Belleau Wood, St. Mihiel and in the Argonne Forest from May to November 1918. With nearly one million troops in the line by the end of the war, the American presence finally convinced the Germans that the war could not be won; they had managed to win a war of attrition with France and Britain, but the influx of an endless supply of American troops meant that there was no way Germany could win. By November 1918, the writing was on the wall and on 11 November 1918, the guns fell silent along the entire line as an armistice was signed, signaling the end of the war.
While white American soldiers fought in their own units in their own part of the line, black troops were relegated to support duty, or sent to the French army to fight under French commanders. Despite the fact that American officers ordered the French not to treat the African-American soldiers with respect—lest they become "uppity" and learn what a non-prejudicial society was like—the French treated the black soldiers with the respect they deserved; the 395th Infantry, a black unit fighting with the French, won 171 commendations for valor. Upon returning home, Jim Crow racism was as rampant as ever in America, and more than 70 returning veterans were lynched in the first year after the end of the war. Still, the experience of black soldiers and the effects of the wartime Great Migration of southern blacks to northern cities had a lasting impact on American society, and sowed the seeds of the Civil Rights Movement.
World War I was a turning point for America economically. With war orders flooding in from Europe, American manufacturers grew rich, and American industrial might began to lead the world. The international financial system set up its capital in New York during this period, and the war catapulted America into a leading role in economic and military affairs.
When President Wilson traveled to Paris for the peace conference that would lead to the Treaty of Versailles, he came armed with his Fourteen Points, an idealistic plan to reorder Europe with the United States as a model for the rest of the world. He failed to gain most of what he wanted as the French and British were more inclined towards a vengeful peace, requiring reparations from Germany, than to any idealistic requests of the United States. The League of Nations, the one victory Wilson managed at the conference, was never ratified by the United States Senate, and, without the United States, it failed as a toothless organization that collapsed in the face of German and Japanese aggression in the 1930s.