Americans greatly affected the end of WWI because they broke the stalemate. Until the entry of the U.S. in 1917, WW1 was in a stalemate. Each side literally traded yards of territory from one day to the next. There was no progress. When the U.S. joined they brought with them a large amount of soldiers. It was more a game of numbers than battles once the U.S. arrived. Germany's position quickly became untenable and well before the armistice, they were asking for peace.
When America Fought in WWI and Became a Global Power. ... Swinging its industrial might and vast manpower behind France and Britain against Germany and its allies on April 6, 1917, the United States tipped the balance of the conflict and marked its own emergence as a global power
