When the USA declared war in April 1917, President Woodrow Wilson sent the American Expeditionary Force (AEF) under the command of General John Pershing to the Western Front. The Selective Service Act, drafted by Brigadier General Hugh Johnson, was quickly passed by Congress.

Under this law, all males between the ages of 21 and 30 were required to register for military service. By 12th September 1918, 23,908,566 men had registered. Around 4,000,000 men were ultimately drafted into the armed services.

More than 2 million troops eventually reached Europe but a large number arrived too late to see any action. The United States forces suffered 264,000 casualties during the war. It has been calculated that 112,432 Americans died. Of these, around 50 per cent died from disease (mainly influenza).