The United Nations was established in 1945 to replace the failed League of Nations and prevent future world wars. It was formed through discussions between world leaders during and after World War II. The UN Charter was signed in 1945 and established the main organs of the UN - the General Assembly, Security Council, Economic and Social Council, Trusteeship Council, International Court of Justice, and Secretariat. The UN aims to maintain international peace and security and promote cooperation between nations. It has played an important role but also faces ongoing calls for reforms to its structures and operations.