At it's height the League of nations supported 58 members
The United States, Germany, and Russia were three major powers that were not members of the League of Nations. The League of Nations lasted from 1919 to 1946.
The League of Nations later turned into the United Nations. So basically the entire U.N. is the League of Nations. This originally consisted of 58 nations, and since I do not want to list them all, then just look up "League of Nations original members" on Bing.
Member nations had to defend other members if they were attacked.
The League of Nations was supposed to do many things, but first and foremost was to prevent another world war, which it failed to do.
The big four involved in The League of Nations were; Woodrow Wilson, George Clemenceau, Vitorio Orlando and David Lloyd George
42 original members of the League of Nations
Art.10 of the League of Nations Covenant (1919) sought to...'respect and preserve against external aggression the territorial integrity and existing political independence of all Members of the League'...
It had no mandate or authority to do so.
There were a number of conservative members of congress who were isolationists. They opposed the League of Nations and they did not want the US to become a member. They believed that by joining the League, the US would be giving up some of our sovereignty to a foreign power.
The League of Nations.
The United States never joined the League of Nations. The loosing countries of World War 1 were not among the initial members but did eventually joined, as did the USSR in 1934. The last nation to join was Egypt, on 26 May 1937.