America entered WWI just 17 months before it finished, and had a minimal effect on it.
In fact, when the US entered the war it was so unprepared was it that the Americans had to rely on the British to provide them with mortars,
machine guns, steel helmets and uniforms. They also had to borrow artillery guns off the French.
The lack of speed with which the Yanks were sent to Europe was later criticised by British PM David Lloyd George. The 1st Division AEF (American Expeditionary Force) landed in France in June 1917. The 2nd Division did not arrive until September and by October 31st, 1917, the AEF only numbered 6,064 officers and 80,969 men. In roughly the same time span in 1914, the British Expeditionary Force (BEF) had got 354,750 men into the field. Nine months after America declared war, there were 175,000 American troops in Western Europe. In the same time span of nine months from 1914 to 1915, Britain had put 659,104 men into the various theatres of war. Therefore, in 1917, despite her strength on paper, America played little part in the war activities of that year.