Despite the fact that United States’ president Woodrow Wilson had won the re-election in 1916 by keeping America out of the war, in April 1917, he declared war on Germany with resolution and detailed war aims. The decision was especially fasten by Germany’s unrestricted submarine policy and the occurrence of the Zimmerman telegram. There is a great discussion over the importance of American entry of the war to the outcome of the war, some historians agree with the statement and the others don’t.

One of the reasons that historians agree with the statement is its creation of psychological pressure for the Germans. When Russia left the war due to series of rebellion and revolution happened, Germany believe that they had the advantage of manpower, which sustained their morale. However, with vigorous troops coming from America, the advantage had canceled out.
Statistics shows that in the month of 1918, a total of 84,889 American soldiers reached the western front, and in July the number rose to 306,350. Germany only had 300,000 replacements for the whole of 1919. Until then, a fresh new army was made available to the Allied force each month.
Not only these American soldiers were send with large numbers, they also brought the energy and enthusiasm the Germans had exhausted. While Germans had fought the war for a few years, these American soldiers had the enthusiasm the Germans exhausted, the number does seem massive respectively. With the massive number of each troop and150,000 newly arrived americans soldiers to the western front each month, the soldiers played a role to pressurise the enemy, also in another point of view, the thought of the Allied force doomed to win reminded other battalion forces the energy to put which the Americans encouraged them to keep fighting.

The arrival not only gave the Germans pressure but also a motive to mutiny which