States first established international organizations to cooperate on specific matters. The International Telecommunication Union was founded in 1865 as the International Telegraph Union, and the Universal Postal Union was established in 1874. Both are now United Nations specialized agencies.

 In 1899, the International Peace Conference was held in The Hague to elaborate instruments for settling crises peacefully, preventing wars and codifying rules of warfare. It adopted the Convention for the Pacific Settlement of International Disputes and established the Permanent Court of Arbitration, which began work in 1902.

The forerunner of the United Nations was the League of Nations, an organization conceived in similar circumstances during the first World War, and established in 1919 under the Treaty of Versailles "to promote international cooperation and to achieve peace and security." The International Labour Organization was also created under the Treaty of Versailles as an affiliated agency of the League. The League of Nations ceased its activities after failing to prevent the Second World War.

 In 1945, representatives of 50 countries met in San Francisco at the United Nations Conference on International Organization to draw up the United Nations Charter. Those delegates deliberated on the basis of proposals worked out by the representatives of China, the Soviet Union, the United Kingdom and the United States at Dumbarton Oaks, United States in August-October 1944. The Charter was signed on 26 June 1945 by the representatives of the 50 countries. Poland, which was not represented at the Conference, signed it later and became one of the original 51 Member States.