Which phrase defines the primary purpose of the North Atlantic Treaty Organization?

The primary purpose of the North Atlantic Treaty Organization (NATO) is to ensure collective defense among its member countries. Founded in 1949, NATO's main goal is to provide mutual military support and deter aggression, primarily against threats from outside the alliance. This is encapsulated in Article 5 of the NATO treaty, which states that an armed attack against one member is considered an attack against all. Through cooperation and defense strategies, NATO aims to promote stability and security in the North Atlantic region.