The United States entered World War I in 1917, specifically declaring war on Germany on April 6 of that year. Prior to this, American involvement was largely characterized by neutrality; however, factors such as unrestricted submarine warfare by Germany and the interception of the Zimmermann Telegram, which revealed Germany's proposal to Mexico to ally against the U.S., shifted public opinion and government stance. The entry of the U.S. provided significant military and economic support to the Allied Powers, contributing to the eventual victory in 1918. This involvement marked a crucial turning point in the war and positioned the United States as a significant global power in the post-war era.