The United States entered World War I when the war had already raged for three years. Both sides, both Allied and Central Powers, were exhausted as the war had become one of attrition and annihilation. When the U.S. entered the war, it not only provided fresh troops and supplies, it brought to bear all its resources on the war effort. The U.S. had no agenda for entering the war; President Woodrow Wilson commented as the war neared an end:
We desire no conquest, no dominion. We seek no indemnities for ourselves, no material compensation for the sacrifices we shall freely make. We are one of the champions of the rights of mankind.
Originally, it had been anticipated that the U.S. would have a token role in the war; in fact when the first American troops landed in France on June 26, 1917, only 14,500 men were part of the landing. The American commander, General John J. "Black Jack" Pershing, soon discovered that the Allies were too weary from the three years of fighting to fight alone, and as a result, one million new troops were conscripted at his request.
American troops were not subject to the battle fatigue which had plagued other troops, and once the U.S. entered the war, the end result was almost assured, even though Germany had gained a slight advantage by the withdrawal of Russia from the war. Reportedly, General Ludendorff wired General von Hindenburg to ask instructions when he learned the U.S. had entered the war, to which von Hindenburg replied "make peace, you idiot!) It is no coincidence that the war ended just more than one year after U.S. entry.