The United States formally entered World War I in 1917, after years of growing tension and public debate regarding involvement in the conflict. The decision was precipitated by several factors, including unrestricted submarine warfare by Germany, which threatened American vessels, and the interception of the Zimmermann Telegram, in which Germany attempted to entice Mexico into joining the war against the U.S. The declaration of war marked a pivotal shift as American forces began to support the Allies. This entry not only provided much-needed resources and manpower but also helped turn the tide in favor of the Allies, contributing to the eventual victory.