What event marked the end of the ineffective League of Nations?

The correct answer is the event that took place during World War II. The League of Nations was created after World War I to promote peace and prevent future conflicts. However, it struggled to enforce its resolutions and was unable to prevent the aggression that led to World War II. The outbreak of the war highlighted the League's inability to maintain international peace and security, resulting in its loss of credibility and effectiveness.

As countries engaged in conflict, it became apparent that the League lacked the ability to respond to crises and enforce its decisions. The failure of the League during this tumultuous time led to its eventual dissolution and the establishment of the United Nations after the war, which aimed to create a more effective framework for international cooperation and peacekeeping. The League's demise can thus be closely associated with the global changes and upheaval brought about by World War II, showcasing its ultimate ineffectiveness in the face of serious global challenges.