The event that led to the establishment of the League of Nations was the end of World War I. Following the devastation of the war, there was a strong desire among leaders to establish a framework to prevent future global conflicts. The League of Nations was proposed in President Woodrow Wilson's Fourteen Points and formally established by the Treaty of Versailles in 1919. It aimed to promote peace and cooperation among countries through diplomacy and collective security. Despite its ambitious goals, the League faced challenges, including the absence of major powers like the United States and its inability to address aggression effectively, ultimately resulting in its dissolution after World War II.