The concept of collective security -- Collective security: a historical journey -- The morphology of collective security -- Triggers, actors and institutions -- Collective security components -- States and collective security -- The United Nations -- Regional organisations -- Private military and security companies -- The settlement of disputes and preventive security -- State-building -- Sanctions -- Military security -- Legal management of collective security -- Law as internal facilitator, regulator or constraint -- Law as external facilitator, regulator or constraint -- The management of normative conflicts -- Accountability in collective security -- Accountability in collective security -- International responsibility and liability -- Individual criminal responsibility.