The League of Nations.
They failed and it ended in WWII. It is theorized that it all started when America wasn't involved in the League of Nations.
The League of Nations.
The League of Nations was viewed by the world as "the league of the victors of World War 1" rather than a fair league for all nations. Most nations ignored the League and their goals therefore the League did little to prevent World War 2. The Treaty of Versailles was also connected to the League of Nations and many nations resented that Treaty. This was a major contributing factor of the reasons for World War 2 being started and fought.
The precursor to the Current United Nations was called the League of Nations. The League of Nations was founded in 1919. When the United Nations was formed in 1945, the League of Nations basically ceased to exist.
Nothing. The League of Nations was the predecessor to the United Nations. (:
There is no League of Nations. We have United Nations
The league of nations was created out of WWI.
The United Nations predecessor organization was the League of Nations which was founded at the end of WW1 as a result of the Treaty of Versailles and managed to attract at its best the participation of 58 countries during 24 September 1934 and 23 February 1935.
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."
League of Nations
At it's height the League of nations supported 58 members