The League of Nations, established after World War I, aimed to promote peace and prevent future conflicts through collective security and diplomacy. Though it had notable successes in resolving smaller disputes and addressing issues like refugee crises and health epidemics, it struggled to enforce decisions due to its lack of a military force and the absence of key powers, such as the United States. The League ultimately failed to prevent aggression from nations like Japan, Italy, and Germany in the 1930s, leading to increased tensions that contributed to the outbreak of World War II.