What year did the United States formally enter World War I?

The United States formally entered World War I in 1917. This decision was influenced by several factors, including unrestricted submarine warfare by Germany, which affected American shipping and safety, and the interception of the Zimmerman Telegram, in which Germany sought to encourage Mexico to join the war against the U.S. The combination of these events created significant public and political pressure for the U.S. to join the conflict. President Woodrow Wilson declared war on Germany on April 6, 1917, marking the official entry of the U.S. into World War I, after years of maintaining a neutral stance since the war began in 1914. This entry had a significant impact on the war's outcome due to the contributions of American troops and resources.