On January 22, 1917, the German government gave notice that unrestricted submarine warfare would be resumed. When five U.S. vessels had been sunk by April, Wilson asked Congress for a declaration of war. Immediately, the government set about mobilizing its military resources, industry, labor and agriculture. By October 1918, on the eve of Allied victory, a U.S. army of over 1,750,000 soldiers had been deployed in France.
The U.S. Navy was crucial in helping the British break the submarine blockade, and in the summer of 1918, during a long-awaited German offensive, fresh American troops, under the command of General John J. Pershing, played a decisive role on land. In November, for example, American forces took an important part in the vast Meuse-Argonne offensive, which cracked Germany's vaunted Hindenburg Line.
President Wilson contributed greatly to an early end to the war by defining the war aims of the Allies, and by insisting that the struggle was being waged not against the German people but against their autocratic government. His famous Fourteen Points, submitted to the Senate in January 1918 as the basis for a just peace, called for abandonment of secret international agreements, a guarantee of freedom of the seas, the removal of tariff barriers between nations, reductions in national armaments, and an adjustment of colonial claims with due regard to the interests of the inhabitants affected. Other points sought to ensure self-rule and unhampered economic development for European nationalities. The Fourteenth Point constituted the keystone of Wilson's arch of peace -- the formation of an association of nations to afford "mutual guarantees of political independence and territorial integrity to great and small states alike."
By the summer of 1918, when Germany's armies were being beaten back, the German government appealed to Wilson to negotiate on the basis of the Fourteen Points. The president conferred with the Allies, who acceded to the German proposal. An armistice was concluded on November 11.
Source: U.S. Department of State