After World War I, the nations of the world formed the League of Nations. This organization was a place where nations could talk through their differences calmly. However, some countries like Germany, Italy and Japan ignored the League and tried to solve their problems through war. Members of the League of Nations did not want to go to war to protect other members and the League failed. A Second World War soon followed.
The Allies of World War II often called themselves "the United Nations" (united against the Axis Powers). After the War, the winners formed a new organization for world peace. On 25th April 1945 in San Francisco, they decided on the name '"United Nations". In June they signed the United Nations Charter saying how the organization would work. The UN was created on 24 October 1945 and its first meeting was held in January 1946. Since 1947 the 24th of October has been called “United Nations Day”.