What effect did America's entry in World War I have?
The entrance of the United States into World War I was a major factor in determining the outcome of the war. Prior to the Americans entering the war, the Allies were, at best, in a stalemate with the Central Powers. Germany was convinced it was close to winning the war. They knew that by resuming the sinking of American merchant ships without warning, the United States would enter World War I on the side of the Allies. Germany believed they could win the war before the United States would become a factor in the fighting and in the war itself.
The entrance of the United States into World War I brought a fresh set of troops into the conflict. Unlike the troops from the Allies and the troops from the Central Powers, our troops hadn’t been fighting since 1914. We were able to supply the Allies with rested troops. We were able to provide the Allies with needed supplies and military materials. The entrance of the United States into World War I was the decisive factor in bringing victory to the Allies over the Central Powers.