The American entry into World War I came in April 1917, after two and a half years of efforts by President Woodrow Wilson to keep the United Statesneutral. Apart from an Anglophile element supporting the British, American public opinion went along with neutrality at first. The sentiment for neutrality was strong among Irish Americans, German Americans and Scandinavian Americans, as well as among church leaders and women. On the other hand, even before World War I broke out, American opinion toward Germany was already more negative than it was toward any other country in Europe. The citizenry increasingly came to see the German Empire as the villain after news of atrocities in Belgium in 1914, and the sinking of the passenger liner RMS Lusitania in May 1915. Wilson made all the key decisions and kept the economy on a peacetime basis, while allowing banks to make large-scale loans to Britain and France. To preclude making any military threat, President Wilson made only minimal preparations for war and kept the United States Army on its small peacetime basis, despite increasing demands for preparedness. However, he did enlarge the United States Navy.
In early 1917, Germany decided to resume all-out submarine warfare on every commercial ship headed toward Britain, realizing that this decision would almost certainly mean war with the U.S. Germany also offered to help Mexico regain territories lost in the Mexican–American War in the Zimmermann Telegram. Publication of that offer outraged Americans just as German U-boats (submarines) started sinking American ships in the North Atlantic. Wilson asked Congress for "a war to end all wars" that would "make the world safe for democracy", and Congress voted to declare war on Germany on April 6, 1917. On December 7, 1917, the U.S. declared war on Austria-Hungary.