As the First World War erupted in Europe in 1914, the United States declared itself neutral. Afterward, the Americans sympathized with the British and French, even though many citizens, especially those from Ireland and Germany, were against the intervention. In 1917, they joined the Allies, adding to the defeat of the "Central Powers". Unwilling to participate in European affairs, the Senate did not approve the Treaty of Versailles (1919), which established the League of Nations, applying a policy of unilateralism, which bordered on isolationism. In 1920, the Women's rights movement gained the approval of a constitutional amendment to grant women the right to vote.