The League of Nations failed in the 1930s because, although its primary mission was to secure world peace, it did not prevent Axis nations from invading and annexing nations and World War II from breaking out. It was weakened by poor global representation, the lack of an armed force of its own and insufficient assurances of collective security.
Although President Woodrow Wilson originally proposed the establishment of the League of Nations at the end of World War I, the isolationist U.S. Senate rejected the proposal, and the United States did not join. Germany was also excluded in the beginning because it had been the aggressor in the war, and Soviet Russia was excluded because it was communist. Later, both countries were admitted. However, the Axis countries of Germany, Italy and Japan all withdrew from the League in the 1930s because of increasing pressure to demilitarize. Japan invaded Manchuria, Italy invaded Ethiopia and Germany invaded and annexed Austria, the Sudetenland and eventually all of Czechoslovakia, and the League of Nations was powerless to prevent any of these aggressive actions from happening.
In December 1939, Russia was expelled from the League for its attack on Finland. During World War II, the League of Nations never met and effectively ceased to function. It was not dissolved formally, however, until April 1946, when the last meeting was held in Geneva. The United Nations, with improved international support, took its place.