Why did the United States Senate reject membership in the League of Nations?

The United States Senate rejected membership in the League of Nations primarily due to concerns that joining the organization would compromise American sovereignty and limit the constitutional authority of Congress to declare war.123

Led by Republican Senator Henry Cabot Lodge, opponents argued that the League’s covenant—specifically Article 10, which mandated collective security—could draw the United States into foreign conflicts without explicit congressional approval. Lodge introduced a series of reservations intended to protect U.S. interests and require congressional consent before the nation could be bound by League decisions.134

The failure to ratify the Treaty of Versailles was exacerbated by a political stalemate. President Woodrow Wilson refused to accept the proposed reservations, viewing them as a nullification of the League's intent. Following a debilitating stroke, Wilson’s rigid stance against compromise prevented the treaty from achieving the two-thirds majority required for ratification in the Senate. Consequently, the United States never joined the League, ultimately returning to a policy of isolationism.14356