Why did some senators oppose the participation of the U.S. in the League of Nations following World War I?

They were afraid that the U.S. would lose some of its autonomy and also get involved in other wars.

http://www.pbs.org/wgbh/amex/wilson/portrait/wp_league.html

Some senators opposed the U.S. participation in the League of Nations following World War I for several reasons. To understand the reasons, we can look into the historical context and the political climate of the time.

1. Sovereignty Concerns: Many senators were concerned that joining the League of Nations would compromise American sovereignty. They feared that participating in the League would involve giving up some control over foreign policy decisions to an international organization.

2. Anti-Entanglement: The opposition also believed in a policy of isolationism and non-interventionism. They did not want the U.S. to get involved in foreign conflicts and alliances, particularly in European affairs. They saw the League as a potential entanglement that would drag America into conflicts that did not directly affect its national interests.

3. Opposition from Senate Republicans: The Treaty of Versailles, which included the provision for the League of Nations, was negotiated by President Woodrow Wilson, a Democrat. Many Republican senators opposed Wilson's foreign policy agenda and considered the League of Nations as a partisan initiative. They viewed the League as an attempt to consolidate power in the presidency and bypass Congress in making foreign policy decisions.

4. Concerns about War Powers: Some senators were concerned that joining the League would lead to the U.S. being dragged into future wars without the consent of Congress. They believed that the treaty's collective security mechanisms could potentially obligate the U.S. to take military action without proper congressional authorization.

Ultimately, the opposition led by Republican senators resulted in the U.S. Senate rejecting the Treaty of Versailles and the League of Nations in 1919. The U.S. did not officially join the League, which impacted the League's effectiveness and later contributed to its weakness in addressing global conflicts, particularly in the lead-up to World War II.