Final answer:
The U.S. Senate resisted membership in the League of Nations because it would have limited the U.S.'s ability to formulate an independent foreign policy and curtailed its constitutional power to declare war. The control that Britain and France had in the League was also a concern for the Senate.
Step-by-step explanation:
The reason the U.S. Senate resisted membership in the League of Nations was because it would have curtailed the U.S.'s ability to formulate an independent foreign policy. The Senate feared that if the United States joined the League, it would be drawn into foreign disputes and lose its constitutional power to declare war. The Senate also objected to the control that Britain and France had in the League. These concerns led to the United States not approving the treaty and not joining the League of Nations, weakening the organization's ability to mediate international disputes.