Collective Security System
Concept Security and Defense Preferred
System in which States collectively respond to any State that breaks or threatens the peace.
Independent referenceNot an official or legal definition
Sources citedSee the sources at the end of this page
Status Under reviewLast updated 11 October 2026
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Definition
In plain language
In a collective security system all member States agree to act together against any one of them that attacks another. The idea is that everyone protects everyone.
Academic definition
Collective security is the principle that peace is maintained by the combined action of all members against an aggressor, in contrast to alliances aimed at a specific outside threat. The League of Nations Covenant (Articles 10 and 16) was the first attempt, and the UN Charter strengthened it by prohibiting force (Article 2(4)), giving the Security Council power to determine threats to the peace and decide on measures (Articles 39 to 42), and requiring Members to carry out its decisions (Article 25). Its operation has been limited by the veto of the permanent members, which led to the General Assembly's 1950 Uniting for Peace resolution.
Classification
- Term type
- Concept
- Category
- Security and Defense
- Subject field
- Security and International Organization
- Subfield
- UN Collective Security
- Difficulty level
- Intermediate
- Grammatical category
- noun phrase
Language variants
- Alternative terms
- system of collective security
- collective security regime
- Non-preferred terms
- not_applicable
- Abbreviations
- not_applicable
- Acronyms
- not_applicable
- Native terms
- not_applicable
- Transliteration
- not_applicable
- Pronunciation
- not_applicable
Context
Legal effect: Binding
Scope
Covers system-wide arrangements to deter and respond to aggression; defensive alliances and ad hoc coalitions are separate and are covered by 'Collective Defense Clause' and 'Coalition of the Willing'.
Legal context
UN Charter Articles 2(4), 24, 25, 39, 41, 42 and 43; the Council's decisions under Chapter VII bind all Members, and Article 103 gives Charter obligations priority over other treaty obligations. The 1950 Uniting for Peace resolution (377(V)) allows the Assembly to act when the Council is deadlocked.
Diplomatic context
Permanent members negotiate resolutions and may veto them, and States debate the legitimacy of Council action and the role of regional organisations.
Institutional context
Centred on the UN Security Council with the General Assembly, regional organisations under Chapter VIII, and the Military Staff Committee.
Historical context
The League of Nations tried the system in the 1920s and 1930s, and the UN in 1945 gave it a stronger legal basis, though Cold War divisions limited its use until the 1990s.
Why it matters
The effectiveness of the system determines whether aggression is deterred by the world community or must be met by individual States and alliances.
Usage
Register: Institutional
Usage note
Do not use 'collective security' for NATO or other alliances; the standard contrast is with 'collective defence'.
Example
Under the collective security system, the Council authorised measures against the State that had invaded its neighbour.
Example scenario
State A invades State B. The Security Council determines that this is a breach of the peace, imposes sanctions and authorises Member States to use force if needed, and all UN Members are bound to implement the decision.
Common misuse
Using it as a synonym for military alliance; collective security is directed at any aggressor within the system, not at an external enemy.
Not to be confused with
- Collective defense clause
- Military alliance
- Balance of power
Sources
- Charter of the United Nations (1945), United Nations, Articles 39-42. un.org
- Official definition. not_found_in_source
- Treaty reference. un.org
- Kelsen, Collective Security under International Law. not_found_in_source
- not_found_in_source. not_found_in_source
Source type: Treaty. Source reliability: Primary.
This entry is an independent reference definition, not an official or legally binding text. Where an official definition exists, it is linked above and is authoritative. Read our methodology.
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