The correct answer is A. To provide for the mutual defense of any member nation against an attack by a non-member
Explanation:
The Nort Atlantic Treaty Organization or NATO is basically an alliance created in 1949 between different European and North American countries that agreed on collective defense if one of the members is attacked by an external country, organization or any other non-member. This means the 29 countries that belong to the NATO will defend each other from an external attack during history the NATO has intervened in different cases including the September 11 attacks through the International Security Assistance Force with troops from different countries of the NATO and the Kosovo Intervention. The previous implies the reason why the NATO was formed was to provide the mutual defense of any member nation against an attack by a non-member.
