The League of Nations was an international organisation founded on 10 January 1920 as a result of the Paris Peace Conference that brought the First World War to its end. It was the first intergovernmental organisation whose principal mission was to keep the whole world in peace. At its greatest extent from 28 September 1934 to 23 February 1935, it had 58 members. However, the US, although involved in the discussions that set up the League was not a member. The League effectively collapsed with outbreak of World War 2 and was replaced by the UN in 1946.

More Info: en.wikipedia.org