Which organization enshrines the principle of collective defence in its Article 5?

The principle of collective defense is a key component of NATO's founding treaty, specifically outlined in Article 5. This article states that an armed attack against one or more NATO members is considered an attack against all members, obligating them to support the member under threat. This principle serves as a critical assurance of mutual defense and security among member states, forming the cornerstone of NATO's purpose as a military alliance.

In contrast, the other organizations mentioned do not have a similar collective defense commitment enshrined in their foundational documents. The United Nations focuses more on maintaining international peace and security and does not require member states to come to each other's defense in the event of an attack. The European Union has some cooperative defense elements but is primarily an economic and political union rather than a military alliance. The World Health Organization, meanwhile, is dedicated to international public health rather than military or defense matters. Therefore, NATO is unique in its explicit articulation of collective defense through Article 5.