The League of Nations (French: Société des Nations) was the predecessor to the United Nations. The League was founded in 1920, after World War I, but failed to maintain peace and prevent World War II. The League had a Council of the great powers and an Assembly of all of its member countries.
The League of Nations was thought up by US President Woodrow Wilson during World War I. It was to be a group of nations that worked together to keep peace. One of the reasons for its downfall was that, after a vote, the US Senate refused to join.