Final answer:
The United States did not join the League of Nations due to concerns over the Treaty of Versailles and the Senate's objections to the organization's structure and control.
Step-by-step explanation:
The United States did not join the League of Nations when it first convened because the U.S. Senate did not approve the Treaty of Versailles, which established the League. Senators were concerned that joining the League would compromise their constitutional power to declare war and objected to Britain and France's control over the organization. As a result, the United States did not become an official signatory of the Treaty of Versailles and did not join the League of Nations.