The historical event that led to the formation of the League of Nations was World War I. The devastation and geopolitical shifts caused by the war underscored the need for an international organization dedicated to promoting peace and preventing future conflicts. In 1919, the League of Nations was established as part of the Treaty of Versailles, aiming to provide a forum for resolving disputes between nations diplomatically rather than through war. Despite its intentions, the League struggled to maintain peace and prevent aggression, leading to its eventual dissolution and the establishment of the United Nations after World War II.