The League of Nations (1919-1946) was established by the Treaty of Versailles after world war one as an attempt to encourage international co-operation and security.
After world war two this body was replaced by the United Nations, originally consisting of 51 nations, and established under the Charter of the United Nations. Currently the UN is composed of 193 member states.
General Assembly - main deliberative organ represented by all member states.
Security Council - international peace and security. Made up of 5 permanent and 10 non-permanent members.
Economic and Social Council - principle organ coordinating economic, social and related work, involving 54 member states.
International Court of Justice - principle judicial organ (see Courts, Tribunals and Cases tab)
Trusteeship Council - Established in 1945, this body oversaw 11 trust territories until their independence was completed in 1994. Now meets only as required.
Secretariat - carries out the day-to-day work of the UN.