CEVAP:

Once a group of States agree that some concerns are to be dealt with institutional mechanisms, they usually sign a treaty establishing a defence pact and declare that an attack against any of them is in fact directed to all of them. The legal basis of such regional organizations is provided by the UN Charter. The Charter, which prohibits threat and use of force in its Article 2/4, permits States to defend themselves against an armed attack individually or collectively (Article 51). More importantly, Article 52, which is the true legal basis of regional security organizations, allows States to establish “regional arrangements or agencies for dealing with” regional and international peace and security, provided that they are “consistent with the Purposes and Principles of the United Nations”.