The UN and Collective Security: the law on the use of force

1. FRAME — Kellogg-Briand to the Charter

The pre-1945 framework was a sequence of failed half-measures. The League Covenant (Articles X–XVI) imposed cooling-off periods, not a prohibition; states retained a residual right to resort to war. The Kellogg-Briand Pact 1928 Article 1 condemned and renounced "recourse to war … as an instrument of national policy". Two defects gutted it: only "war" was prohibited (Manchuria 1931 was framed as an "incident"); no enforcement machinery (Abyssinia 1935 — partial, unenforced sanctions). The interwar regime was aspiration without teeth.

The Charter responds with two obligations. Article 2(3) requires peaceful settlement. Article 2(4) is the operative prohibition: Members "shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations". The architecture is restrictive: a comprehensive ban subject to two exceptions (Article 51; Chapter VII), policed by the Security Council. Nicaragua para 190 confirms jus cogens character.

2. EXPLAIN — the scope of Article 2(4)

Five interpretive battlegrounds run through Article 2(4).

• "International relations". Article 2(4) does not reach genuine internal conflict, but assistance internationalises it. Nicaragua paras 202–209: intervention on behalf of rebels breaches Article 2(4) and non-intervention. Intervention by invitation from the recognised government remains lawful (Yemen 2015–, Saudi-led coalition). The line turns on effective government and genuineness of consent.
• "Threat" of force. Nuclear Weapons AO 1996 paras 47–48: a threat is "a signalled intention to use force if certain events occur". Possession is not per se a threat; military manoeuvres may qualify (Nicaragua para 227).
• "Force". Confined to armed force (Friendly Relations Declaration, GA Res 2625 (XXV) 1970). The Cold War debate on economic coercion was resolved against it: economic measures fall under non-intervention, not Article 2(4).
• "Against territorial integrity … or otherwise inconsistent". The permissive reading (UK in Corfu Channel 1949, claiming minesweeping threatened "neither the territorial integrity nor the political independence of Albania") was rejected. Armed Activities 2005 para 148: Article 2(4) does not allow force "to protect perceived security interests".
• Jus cogens. Nicaragua para 190 — peremptory; no treaty or persistent objection licenses unilateral force outside the two exceptions.

3. Article 51 — the right of self-defence

Article 51 preserves "the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations". Nicaragua para 176 affirms a parallel customary right.

Armed attack — gravity threshold. Nicaragua para 191 distinguishes "the most grave forms of the use of force (those constituting an armed attack)" from less grave forms. Oil Platforms (Iran v US) 2003 paras 51, 64, 72: the Court "does not exclude the possibility that the mining of a single military vessel might be sufficient" to trigger Article 51, but the US failed to prove Iranian responsibility for the Samuel B Roberts mining. Strict standard of proof on the defending state.

Indirect armed attack. Nicaragua para 195 (with Article 3(g) of GA Resolution 3314 (XXIX) 1974): sending armed bands of sufficient "scale and effects" qualifies. Para 230: "the provision of arms to the opposition in another State" does not constitute an armed attack, however much it breaches Article 2(4). Hold the line between the categories.

Necessity and proportionality. The Caroline Incident 1837 requires "a necessity of self-defence, instant, overwhelming, leaving no choice of means and no moment for deliberation"; the response must be "kept clearly within" that necessity. Affirmed as customary in Nicaragua para 194; applied in Armed Activities para 147 — Uganda's seizure of airports and towns "many hundreds of kilometres from Uganda's border would not seem proportionate".

Anticipatory v pre-emptive self-defence. Most scholarship (Bowett, Dinstein) accepts anticipatory self-defence against a strictly imminent attack. Pre-emptive action against non-imminent threats — the US National Security Strategy 2002 ("Bush Doctrine") openly adapting "the concept of imminent threat" to rogue-state and WMD cases — is different. The ICJ did not endorse it; Wall AO and Armed Activities left the question open. The general view (Gray, Byers) is that the Bush Doctrine is not customary law.

Collective self-defence. Nicaragua paras 195, 199, 232: three preconditions — armed attack on the victim, victim's declaration, and request for assistance. Reporting: failure to report has evidential value — Nicaragua para 200; Armed Activities para 145.

Self-defence v non-state actors. UNSC Resolutions 1368 (2001) and 1373 (2001) recognised the inherent right after 9/11; Operation Enduring Freedom was widely treated as lawful. The ICJ has been cautious. Wall AO 2004 para 139 reads Article 51 as recognising self-defence "in the case of armed attack by one State against another State"; the separate opinions of Higgins, Kooijmans and Buergenthal disagreed. Armed Activities para 146 leaves open "whether and under what conditions contemporary international law provides for a right of self-defence against large-scale attacks by irregular forces".

What has emerged in practice is the "unable or unwilling" test — clearest in the US Power letter of 23 September 2014 justifying strikes against ISIS in Syria: self-defence is permissible "when … the government of the state where the threat is located is unable or unwilling to prevent the use of its territory for attacks". Contested — Reinold defends; Gray and O'Connell reject it for thin practice and hostile opinio juris. Register the contestation, do not assert as settled.

4. Chapter VII — collective measures

The procedure is a step-cascade. Article 39: Council determination ("threat to the peace, breach of the peace, or act of aggression"). Article 40: provisional measures. Article 41: non-forcible measures (sanctions). Article 42: force where Article 41 "would be inadequate". Articles 43, 46, 47: Member States to make forces available under "special agreement", planned by a Military Staff Committee — never concluded, never operationalised. The Cold War froze the architecture.

The workaround is the "all necessary means" formula. UNSC Resolution 678 (1990) on Iraq/Kuwait ("Authorises Member States … to use all necessary means") is the template. UNSC Resolution 1973 (2011) extended it to civilian protection in Libya. Enforcement is contracted out to willing states, not commanded.

The veto problem. P5 deadlock — Cold War, then Syria, Ukraine, Gaza. The GA's "Uniting for Peace" Resolution 377 (V) 1950 claims a residual GA capacity to recommend collective measures where the Council is deadlocked. Legal status contested — Article 24 assigns "primary", not exclusive, responsibility to the Council — and recent Emergency Special Sessions have shifted political weight without producing binding authorisation.

5. Key cases and instruments

6. Beyond-Charter exceptions

States periodically advance further exceptions. None has settled into customary law.

Humanitarian intervention. NATO Kosovo (1999) was unauthorised and justified on humanitarian grounds. The UK's 2000 written ministerial statement (restated in the 2018 Syria chemical-weapons legal position) identified three conditions: extreme humanitarian distress on a large scale, no practicable alternative, minimum force necessary. Rejected by most states (NAM 2000) and most scholarship as not customary; invoked persistently. Policy, not doctrine.

Responsibility to Protect. The 2005 World Summit Outcome paras 138–139 routed collective response "through the Security Council". R2P is not an autonomous legal basis; it operates through Chapter VII. UNSC 1973 (2011) is often described as its first operationalisation; the post-Libya Russian/Chinese backlash has stalled the doctrine on Syria.

Rescue of nationals abroad. Entebbe 1976. UK recognises a limited form (necessity, proportionality, imminent danger). Most scholarship: not yet customary; some fold it into a strict reading of self-defence. Exceptional and easily abused.

7. Academic voices

Self-defence is permitted "if an armed attack occurs". Anticipation must answer to a strict requirement of imminence; pre-emption against speculative future threats is not lawful self-defence under the Charter as it stands.

— Yoram Dinstein, War, Aggression and Self-Defence (6th ed CUP 2017) — paraphrased.

The "unable or unwilling" doctrine has been advanced as if it were customary; but state practice is thin, the opinio juris of most states is sceptical, and the Court has declined to endorse it. To present it as settled law is to conflate the assertions of a small group of powerful states with the practice of the international community.

— Christine Gray, International Law and the Use of Force (4th ed OUP 2018) — paraphrased.

The post-Cold War period saw a re-pricing of the Charter's prohibitions: humanitarian intervention, anticipatory self-defence, authorisations stretched. Some adjustments are productive accommodations; others are unilateral assertions in the language of legality. The framework holds, but only because it is contested.

— Thomas Franck, Recourse to Force (CUP 2002) — paraphrased.

The Bush Doctrine was not law but a bid to make law. To accept it as customary on the basis of one or two assertive states would be to let the most powerful legislate unilaterally — exactly what the discipline of customary international law exists to resist.

— Michael Byers, War Law (Atlantic 2005) — paraphrased.

Self-defence against non-state actors operating from the territory of a state unwilling or unable to suppress them can be reconciled with Article 51 — provided the attack meets the gravity threshold and the response is necessary and proportionate. The alternative is a sanctuary rule that rewards state weakness with immunity.

— Theresa Reinold, "State Weakness, Irregular Warfare, and the Right to Self-Defense" (2011) 105 AJIL 244 — paraphrased.

8. Common pitfalls

9. Exam answer skeleton

1. FRAME. Pre-1945 failure (Kellogg-Briand 1928; Manchuria; Abyssinia). Charter architecture: Article 2(3); Article 2(4) as jus cogens (Nicaragua 190); Article 51; Chapter VII.
2. EXPLAIN — Article 2(4). "International relations" (Nicaragua 202–209); "threat" (Nuclear Weapons AO 47–48); "force" armed not economic; comprehensive prohibition (Corfu Channel; Armed Activities 148).
3. EXPLAIN — Article 51. Inherent (176); armed-attack threshold (191; Oil Platforms 51, 64, 72); indirect armed attack and Article 3(g) (195); not mere arms supply (230); necessity/proportionality (Caroline; 194; Armed Activities 147); reporting (200; 145); collective preconditions (195, 199, 232); anticipatory v pre-emptive; non-state actors (1368/1373; Wall 139; Armed Activities 146; unable-or-unwilling).
4. EXPLAIN — Chapter VII. Articles 39–42; Article 43/47 dead-letter; "all necessary means" (UNSC 678; 1973); veto deadlock; Uniting for Peace.
5. EVALUATE. Gray/Dinstein/O'Connell sceptical; Reinold/Franck accommodating. Position: Article 2(4) peremptory; ICJ policed expansion narrowly; unable-or-unwilling not customary; framework holds because contested.
6. CONCLUDE. Framework restrictive; practice contested; gap is the terrain. Defer Iraq 2003 / Iran 2026 to Topic 10.

10. Checklist

• Cited Nicaragua with paragraphs (176, 190, 191, 195, 199, 200, 230).
• Anchored every claim in a Charter article and a paragraph of authority.
• Distinguished use of force from armed attack and indirect armed attack from mere assistance.
• Used Oil Platforms (51, 64, 72) on gravity threshold and proof.
• Used Wall AO 139 and Armed Activities 146 on non-state actors; named the Higgins/Kooijmans/Buergenthal critique.
• Quoted Caroline ("instant, overwhelming … no moment for deliberation"); tied to Nicaragua 194 and Armed Activities 147.
• Distinguished anticipatory (Caroline) from pre-emptive (NSS 2002; not customary).
• Set out Chapter VII cascade; cited UNSC 678 (1990) and 1973 (2011).
• Took a position on unable-or-unwilling and humanitarian intervention/R2P, with named scholars.