Why did the League of Nations fail to gain U.S. Senate approval?

The League of Nations failed to gain U.S. Senate approval primarily due to concerns regarding foreign conflict and the potential for automatically entangling the United States in international disputes without Congressional consent. Many senators feared that joining the League would compromise U.S. sovereignty and lead to involvement in conflicts that did not align with American interests. This apprehension was rooted in the desire to maintain a policy of isolationism and was significantly influenced by the legacy of World War I, which many Americans were eager to avoid repeating.

The League's covenant required member nations to be committed to collective security, which meant that the U.S. might have been obligated to support military actions or political interventions without the Senate's prior approval, undermining Congressional authority in matters of war and peace. These concerns were particularly pronounced among Republican senators, who were wary of President Woodrow Wilson’s vision for an active role in world affairs through this organization.

While issues related to funding or a lack of international support may have played secondary roles, the primary objection centered around the fear of losing control over U.S. foreign policy, which ultimately led to the rejection of the League by the Senate.