DEFINITION

"The Members of the League undertake to respect and preserve as against external aggression the territorial integrity and existing political independence of all Members of the League. In the case of any such aggression or in case of any threat or danger of such aggression the Council shall advice upon the means by which this obligation shall be fulfilled."

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. In other words, it is an attempt to guarantee the territorial integrity and political independence of member states against aggression. (COLLECTIVE SECURITY)

SIGNIFICANCE

This article was the reason why United States didn't join the League of Nations. The US senate refused to officially approve the Treaty of Versailles because of many senators had objections against the Article X. Their reason was that by ratifying the document, the international contract would require the United States to defend or at least give support to the countries that were in the League of Nations when they were attacked. This objection led to a thought of that it's best not to involve in any of international conflicts unnecessarily.
Due to the Article X, many of other nations in the League had the same objections within their countries.