quality:correction
United States enters the war

The United States was a major supplier of war material to the Allies but remained neutral in 1914, in large part due to domestic opposition. The most significant factor in creating the support Wilson needed was the German submarine offensive, which not only cost American lives but paralysed trade as ships were reluctant to put to sea.

On 6 April 1917, Congress declared war on Germany as an "Associated Power" of the Allies. The US Navy sent a battleship group to Scapa Flow to join the Grand Fleet, and provided convoy escorts. In April 1917, the US Army had fewer than 300,000 men, including National Guard units, compared to British and French armies of 4.1 and 8.3 million respectively. The Selective Service Act of 1917 drafted 2.8 million men, though training and equipping such numbers was a huge logistical challenge. By June 1918, over 667,000 members of the American Expeditionary Forces (AEF) were transported to France, a figure which reached 2 million by the end of November.

Despite his conviction that Germany must be defeated, Wilson went to war to ensure the US played a leading role in shaping the peace, which meant preserving the AEF as a separate military force, rather than being absorbed into British or French units as his Allies wanted. He was strongly supported by AEF commander General John J. Pershing, a proponent of pre-1914 "open warfare" who considered the French and British emphasis on artillery misguided and incompatible with American "offensive spirit". Much to the frustration of his Allies, who had suffered heavy losses in 1917, he insisted on retaining control of American troops, and refused to commit them to the front line until able to operate as independent units. As a result, the first significant US involvement was the Meuse–Argonne offensive in late September 1918.