Isolationism: Many Americans were opposed to becoming involved in foreign affairs and believed that the United States should focus on its domestic affairs.
Concerns about the League of Nations: Some Americans were concerned about the power and scope of the League of Nations, fearing that it would infringe on US sovereignty.
Opposition to the Treaty of Versailles: Many Americans felt that the Treaty of Versailles was too harsh on Germany and would lead to future conflict.
Political opposition: President Woodrow Wilson, who had negotiated the Treaty of Versailles, was a Democrat, and the Republican Party was opposed to the treaty.
As a result of the Senate's rejection of the Treaty of Versailles, the United States did not join the League of Nations and instead pursued a policy of isolationism in the years following World War I.