Here is quirky video outlining the reasons why the League of Nations failed.

The League of Nations could not solve conflicts if the member protagonists did not cooperate and follow the rules agreed upon.

During the 1920’s the League repeatedly failed to maintain world peace in many relatively small-scale conflicts.

In the 1930’s, however, the League was unable to resolve two major problems – Japanese expansion in Manchuria and Italian invasion of Abyssinia. 

With the onset of WWII, the League of Nations essentially folded.