Definition
A system in which states collectively respond to threats to international peace, ideally through a broadly inclusive institutional framework. This is distinct from collective defence, as in NATO.
TERMINOLOGY NOTE
Distinction: collective security responds to threats through broadly inclusive institutions; collective defence protects members of a defined alliance.
Theoretical Context
Collective security calls for a broadly inclusive institutional response to threats to peace, irrespective of an aggressor's identity. The UN system illustrates the ambition, while veto politics and enforcement limits affect practice. It is distinct from defence obligations restricted to alliance members.