The United States failed to join the League of Nations because it was not interested in being bound by international law, and because it wanted to reserve the right to intervene militarily in other countries’ affairs.
The United States had just come out of a long and costly war, and was in no mood to get involved in another one. The Senate was controlled by isolationist Republicans who were opposed to US involvement in any international organization. Many Americans were suspicious of the League of Nations because it was set up by Woodrow Wilson, a Democrat. The League of Nations was seen as powerless to stop aggression, and the US was not prepared to put its troops under the command of a foreign body. There was also a feeling that the League of Nations would be dominated by Britain and France, and the US would have no influence. In the end, the Senate refused to ratify the Treaty of Versailles, which included the League of Nations, and the US never joined.
The League of Nations was not a success, and was unable to prevent the outbreak of World War II.
