The Treaty of Versailles, negotiated at the end of World War I, included provisions for a League of Nations—an international organization to promote peace. Although President Wilson campaigned aggressively for U.S. participation, some members of Congress firmly opposed involvement, and the U.S. Senate did not consent to ratify the treaty. Not until 1945, with the creation of the United Nations after World War II, did the U.S. join an international organization to promote cooperation and peaceful resolutions of conflict.