United Nations (UN)An association of independent states formed in 1945 by 51 states as a successor to the League of Nations. The UN aims to maintain peace and international cooperation as well as to promote social development and human rights; has headquarters in New York City. At the end of World War II, the United Nations was established with the aim of preventing further devastating wars. It is a member-based international organization open to all legitimate sovereign states in the international community. While it has a broad and expanding mandate that changes with the times, maintaining international peace and security remains a central aim.