Though World War I began in Europe in 1914, the United States did not enter the war until 1917. What was the primary reason for this delay?

a. The United States had no allies at the time among the European nations.
b. The United States saw the war as a European problem and thus stayed clear of intervention.
c. The United States advocated a policy of isolationism and neutrality until its shipping was directly attacked by Germany.
d. The United Nations had forbidden the United States to intervene.
e. The United States did not have the military personnel or equipment to fight a major war.