I agree to a small extent that the failure of the League of Nations was the most important factor that caused the Second World War. There were other important factors such as Hitler's expansionist policy and the appeasement policy adopted by the Allies.

The failure of the League of Nations was an important cause of the Second World War. The League of Nations did not have the USA as a permanent member and hence it was unable to fulfil its aims of discouraging aggression from any nation or encourage nations to disarm. The League of Nations did not have an army of its own and its members were not committed to working together through the League to settle conflicts. Hence Germany could take the opportunity to rearm and reoccupy the lands lost through the Treaty of Versailles and as a result the League of Nations was not effective...