UN Charter and the Use of Force

The UN Charter generally forbids states from threatening or using armed force in their international relations. Article 2(4) prohibits force against another state’s territorial integrity or political independence, or otherwise inconsistently with UN purposes. This broad non-use of force principle is also recognised as customary international law.

What the prohibition covers

The prohibition applies to both the actual use of armed force and an unlawful threat to use it. Its wording is not confined narrowly to territorial conquest because it also covers force otherwise inconsistent with UN purposes.

• Force generally means armed force; economic or political pressure is governed by other international rules rather than Article 2(4) itself.
• The rule principally regulates force used by one state in international relations, while international humanitarian law separately governs conduct once an armed conflict exists.
• The ICJ’s Nicaragua judgment, 1986 affirmed that the prohibition exists independently as customary international law.

Charter-based lawful uses of force

The Charter preserves two central routes for lawful force: collective action authorised by the Security Council and individual or collective self-defence.

• Under Articles 39 and 42, the Security Council may determine a threat to peace, breach of peace or act of aggression and authorise military action when non-military measures are inadequate.
• Under Article 51, a state may exercise individual or collective self-defence if an armed attack occurs, until the Security Council has taken necessary measures.
• Self-defence must satisfy the customary requirements of necessity and proportionality, and measures taken must be reported immediately to the Security Council.
• Under Article 53, regional arrangements cannot undertake enforcement action without Security Council authorisation, subject to the Charter’s historical enemy-state wording.

Important boundaries

• Military action undertaken with the valid consent of the territorial state is generally not prohibited, provided it remains within the consent granted.
• Not every unlawful use of force reaches the higher threshold of an armed attack that activates Article 51 self-defence.
• The Charter contains no express exception permitting unilateral force solely for humanitarian purposes; collective action must operate through the Charter framework.
• Armed reprisals that are punitive rather than necessary and proportionate self-defence are prohibited.