The United States never joined the League of Nations. This was one of the reasons why the League of Nations wasn’t successful in accomplishing its goals.
Some United States senators were opposed to parts of the charter of the League of Nations. The part that raised the most concern was the provision requiring member nations to help with actions, either military or non-military, against countries that failed to comply with requests made by the League of Nations. These senators believed this would limit flexibility in foreign policy and that the United States might have to become involved in actions that didn’t directly affect the United States. The senators were also concerned we might have to take actions against another country that wouldn’t be in the nation's best interests. They asked President Wilson to negotiate some changes. When he refused, the United States didn’t join the League of Nations. We also didn’t ratify the Versailles Treaty because the League of Nations was part of that treaty.