Final answer:
The U.S. Senate did not ratify the Treaty of Versailles and the League of Nations because they were concerned about the war-making power of Congress and the loss of sovereignty that would come with joining the League.
Step-by-step explanation:
The U.S. Senate did not ratify the Treaty of Versailles, as well as the League of Nations, primarily because the treaty questioned the war-making power of Congress and limited the United States' sovereign control over its military actions. The Senate, dominated by the Republican Party at the time, was concerned that joining the League of Nations would draw the nation into foreign conflicts and undermine their constitutional power to declare war.