Following WWI, President Woodrow Wilson - in an effort to avoid another world war - suggested the League of Nations: a forum through which the world's powers could discuss matters and provide assistance to threatened nations. Ideally, the world would approach a status of peace. However, the League was inefficient, with state actors lacking incentive to assist those threatened nations. To that end, Wilson neglected those Powers in the US Constitution that are granted to Congress. Among those are the rights to make treaties and declare war. Thus, the US could not join the League of Nations, a committe that would eventually be terminated and replaced by the United Nations.
42 original members of the League of Nations
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.
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.
E-JAM
The United States, Japan and Italy
Original Answer: Because they are decades away. Improved: The United Nations are not a country. They couldn't have "joined" the League of Nations. The League of Nations was the predecessor of the United Nations - the League of Nations failed, and so, many years later in 1942 (I believe it was that year) they founded the United Nations as an improved "League of Nations."
Member nations had to defend other members if they were attacked.
The Iroquios, the Haudenosaunee in their own language, are a league or confederation of tribes or nations, not a single tribe. The original members of the league were the Mohawk, Oneida, Onondaga, Cayuga and Seneca nations, later joined by the Tuscarora.
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
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'...