The United States entered World War I in 1917, officially declaring war on Germany on April 6 of that year. U.S. involvement was prompted by several factors, including unrestricted submarine warfare by Germany, which threatened American shipping, and the interception of the Zimmermann Telegram, in which Germany proposed a military alliance with Mexico against the United States. American entry into the war provided much-needed manpower and resources to the Allied Powers, significantly contributing to the eventual victory over the Central Powers. This engagement marked a pivotal moment in U.S. foreign policy, transitioning towards greater involvement in global conflicts.