The United States' decision to join the fight in World War I represented a break from its longstanding policy of neutrality. Prior to entering the war in 1917, the U.S. had maintained a position of isolationism, avoiding involvement in European conflicts and diplomatic entanglements. Many Americans believed in the idea of staying clear of the affairs of other nations, which was deeply rooted in the country's founding principles.
Several factors contributed to the shift in this policy, including unrestricted submarine warfare by Germany, the interception of the Zimmermann Telegram which revealed German proposals to Mexico for an alliance against the U.S., and the desire to protect American interests and promote democracy. The entry of the U.S. into the war marked a significant change in its foreign policy and increased its role on the global stage.