Why was the United States seat on the League of Nations Council never filled?

The United States seat on the League of Nations Council was never filled because the U.S. Senate refused to ratify the Treaty of Versailles, which included the Covenant of the League of Nations.1

While President Woodrow Wilson was a primary architect of the League, he faced significant opposition in the Senate from those who feared that joining the organization would compromise U.S. national sovereignty and entangle the country in foreign conflicts. Led by Senator Henry Cabot Lodge, many senators insisted on adding reservations to the treaty—specifically regarding Article 10, which required members to preserve the independence of other nations.231

Wilson refused to accept these compromises, and the Senate failed to achieve the two-thirds majority required for ratification in votes held in 1919 and 1920. Following the 1920 presidential election, which resulted in a victory for Warren G. Harding and a return to isolationism, all hopes for U.S. membership in the League were effectively ended.13