How did the US contribute to World War I?

The contribution of the United States was decisive in turning the conflict in favor of the Allied Powers. Led by President Woodrow Wilson, the US initially tried to maintain neutrality during the war but struggled to stay neutral and maintain trade relations with the belligerents. The US entered the war largely as a consequence of the German decision to resume unrestricted submarine warfare in 1917, but the US did not become militarily involved until the late fall of that year. At that point, the nation sent an expeditionary force comprising millions of young men to enter the fight. American forces were at the vanguard of the enormous and costly Meuse-Argonne offensive that proved pivotal in forcing the Germans to the bargaining table. In general, the addition of fresh American troops—and especially supplies—reinvigorated the Allies, who had been mired in a stalemate with the equally exhausted German Army for more than three years by the time the United States intervened. Having entered the war, the United States took a leading role in managing the peace process that followed, though the nation refused to join the League of Nations in the war's aftermath.
https://history.state.gov/milestones/1914-1920/wwi