The main reason for the U.S. entry into World War I was the unrestricted submarine warfare declared by Germany, which threatened American lives and commerce. The sinking of RMS Lusitania in 1915, killing 128 Americans, and continued attacks on ships led to growing public outrage. Additionally, the interception of the Zimmermann Telegram, in which Germany proposed a military alliance with Mexico against the U.S., further galvanized American support for entering the war. On April 2, 1917, President Woodrow Wilson asked Congress to declare war, framing the conflict as a struggle to make the world safe for democracy.