On April 6, 1917, the United States formally declared war on Germany and entered World War I. The decision followed months of rising tension over submarine warfare and the Zimmermann Telegram. Many Americans had favored neutrality, but attitudes shifted as attacks on shipping continued. Once at war, the U.S. mobilized millions of soldiers and redirected its economy toward the conflict. American forces and supplies helped break the stalemate on the Western Front. The war’s end reshaped Europe and left the U.S. with a larger role on the world stage.
