United States Enters World War I

Context

The First World War had raged in Europe since the summer of 1914, pitting the Allied powers of Britain, France, and Russia against the Central Powers led by Germany and Austria-Hungary. The United States under President Woodrow Wilson maintained a policy of neutrality, though American banks and manufacturers extended substantial loans and supplies to the Allies while German submarine attacks on Atlantic shipping repeatedly tested that stance. Incidents such as the sinking of the Lusitania in 1915 and the exposure of German diplomatic intrigues heightened public anger without immediately altering official policy.

What Happened

By early 1917 Germany had resumed unrestricted submarine warfare, sinking several American merchant vessels, while British intelligence had intercepted and shared the Zimmermann Telegram proposing a German-Mexican alliance against the United States. On April 2 Wilson addressed a joint session of Congress, describing the German campaign as “warfare against mankind” and asking legislators to recognize a state of war. The Senate approved the resolution two days later by a vote of 82 to 6. Early on the morning of April 6 the House of Representatives concurred 373 to 50, and Wilson signed the declaration into law that same day.

Aftermath

American mobilization began at once, with the Selective Service Act passed in May to build an army that would eventually send more than two million troops to France under General John J. Pershing. Industrial production shifted rapidly toward war materiel, and the United States extended large credits to its new allies while severing remaining ties with the Central Powers. In December 1917 Congress also declared war on Austria-Hungary.

Legacy

U.S. entry supplied the manpower, financing, and industrial capacity that helped tip the military balance toward the Allies, contributing to the armistice of November 1918. The experience propelled the United States onto the world stage, shaped the Treaty of Versailles and the short-lived League of Nations, and prompted lasting changes in American foreign policy, federal authority, and domestic politics including accelerated momentum for women’s suffrage.