Article X of the Covenant of the League of Nations is the section calling for assistance to be given to a member that experiences external aggression. It was signed by the major Peacemakers (Allied Forces) following the First World War, most notably Britain and France. Due to the nature of the Article, Woodrow Wilson was unable to ratify his obligation to join the League of Nations, as a result of strong objection from United States politicians.
Republican opposition in the United States
Although US President Woodrow Wilson had secured his proposal for a League of Nations in the final draft of the Treaty of Versailles, the U.S. Senate refused to consent to the ratification of the Treaty. For many Republicans in the Senate, Article X was the most objectionable provision. Their objections were based on the fact that, by ratifying such a document, the United States would be bound by international contract to defend a League of Nations member if it was attacked. Henry Cabot Lodge from Massachusetts and Frank B. Brandegee from Connecticut led the fight in the US Senate against ratification, believing that it was best not to become involved in international conflicts. Under the United States Constitution, the President of the United States may not ratify a treaty unless the U.S. Senate, by a two-thirds vote, gives its advice and consent. Because the Senate would not support ratification, the U.S. never joined the League of Nations, hampering the League's credibility as a mediator of world conflict.