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.
