Collective security is an agreement and system whereby states will act together to deter or stop the attacking state or states, in which an attack on a member state will be considered as an attack on all member states. The aim of Collective Security is to establish common defense mechanisms to maintain peace and ensure international order. Organizations such as NATO and the United Nations are also based on this principle.

• Claude, I. L. (1984). Swords into plowshares: The problems and progress of international organization (4th ed.). Random House.