Resistance to a United States Senate ratification of the Treaty of Versailles was based on several arguments, but the greatest degree of opposition concerned the Treaty's League of Nations Covenant Article 10. This article gave the League of Nations the power to pursue war as a remedial action without the need for a prior vote of consent by the U.S. Congress. The leader of the Senate opposition to ratification, Henry Cabot Lodge, viewed Article 10 as an infringement upon American sovereignty because it would allow foreign powers in the League of Nations to hold the U.S. to a defense of the Collective Security Agreement without a prior congressional vote on a declaration of war.
Another source of opposition to the Treaty of Versailles came from those senators whose constituencies contained significant numbers of German-Americans. The punitive actions against Germany set forth in the treaty were viewed as harsh and unrealistic by many in both the political and the private realm. Others felt that the treaty favored the British Empire and sought to strengthen and expand its various colonial holdings. Complicating the issue was the position of U.S. President Woodrow Wilson, one of the treaty's advocates and staunchest supporters of the creation of the League of Nations, who was facing a Senate controlled by the members of the Republican Party who viewed him as both an idealist and a political enemy.