The United Nations was founded in the triumph of the world anti-fascist war. The name of the United Nations was put forward by American President Roosevelt. On January 1, 1942, representatives of 26 countries, including China, the United States, Britain and the Soviet Union, who were fighting against German, Italian and Japanese fascists, issued the Declaration of the United Nations in Washington. On April 25, 1945, representatives from 5 countries held the "United Nations Conference on International Organizations" in San Francisco, USA. On June 16th, representatives of 5 countries signed the Charter of the United Nations, and Poland signed it later. On October 24th of the same year, after the Republic of China, France, the League of Soviet Socialist Republics, the United Kingdom of Great Britain and Northern Ireland, the United States of America and most other signatory countries submitted their instruments of ratification, the Charter came into effect and the United Nations was formally established. In 1947, the United Nations General Assembly decided that October 24th was the United Nations Day.

From January 1th to February 14th, 1946, the first phase of the first United Nations General Assembly was held in London. Representatives of 51 founding Member States attended the meeting, and the United Nations organizational system officially began to operate.