The decision by the United States to not ratify the Treaty of Versailles led to problems in the world that eventually created tensions.
The United States didn’t ratify the Versailles Treaty because some United States Senators were concerned that we might have to get involved in conflicts that weren’t in our best interests. This was required by the charter of the League of Nations which was part of the Versailles Treaty. They asked President Wilson to accept amendments to the charter of the League of Nations which would exempt us from having to get involved in any actions recommended by the League of Nations if we felt these actions weren't in our best interests. When President Wilson refused to do this, the Senate didn’t ratify the Versailles Treaty.
Since we didn’t ratify the Versailles Treaty, we also didn’t join the League of Nations. The League of Nations was created to help prevent conflicts from arising. There were many issues with the League of Nations. One issue was that it didn’t have enough power to enforce its actions. Another issue was that the United States didn’t join the organization.
As a result, when Germany, Japan, and Italy began to take aggressive actions in the 1930s, the League of Nations wasn’t able to do much about these actions. This created tensions as the Allies grew more concerned about what was happening in the world. Because the League of Nations was weak and ineffective, and because the Allies were dealing with the effects of the Great Depression, they couldn’t do much to stop these actions that Germany, Japan, and Italy were taking.
The failure of the United States to ratify the Versailles Treaty and to join the League of Nations contributed to the growing tensions in the world that eventually led to the start of World War II.