biggest failure was the united states didnt join the league of nations even though it was originally an american idea. germany and russia didnt join either
league didnt act as a team:
Britain and France, the two most influential members, ignored the League in their efforts to appease Hitler - actions that arguably led to the outbreak of the Second World War.
bbc
world war 2 happened. league of nations was set up to prevent wars
lumenlearning
Some of the successes include the Åland Islands crisis and the Upper Silesia incident
iplorg
successful in small ways in the 1920s, stopping small wars and improving lives
johndclarenet
success in that it did set a precendent for the united nations in the future