The main purpose of the League of Nations, formed after World War I in 1920, was to promote peace and prevent future conflicts through collective security and diplomacy. The League aimed to ensure that disputes between nations would be resolved through negotiation and arbitration rather than warfare. It also sought to address humanitarian issues, promote disarmament, and foster economic and social cooperation among member states. However, the League ultimately struggled to maintain authority and enforce its resolutions, leading to its ineffectiveness in preventing further aggression, which contributed to the outbreak of World War II.