The Formation of the United Nations, 1945 On January 1, 1942, representatives of 26 nations at war with the Axis powers met in Washington to sign the Declaration of the United Nations endorsing the Atlantic Charter , pledging to use their full resources against the Axis and agreeing not to make a separate peace. The United Nations (UN) was the second multipurpose international organization established in the 20th century that was worldwide in scope and membership. Its predecessor, the League of Nations, was created by the Treaty of Versailles in 1919 and disbanded in 1946. United Nations (UN), international organization established on October 24, 1945.