Multiple choice One major reason the League of Nations failed was that it was not included in the Versailles Treaty lacked the support of many of the major world powers was controlled by communist Russia frightened many nations with its large military Reveal answer Fill a bubble to check yourself B Correct answer Explanation The League of Nations was significantly weakened because the United States never joined, and other major powers were either not members or withdrew. This lack of collective support made it difficult for the League to enforce its decisions.