The Meaning of Collective Self-Defence
The Four Categories of Collective Self-Defence
785. The phrase ‘individual or collective self-defence’, as used in Article 51 of the Charter of the United Nations (quoted supra 521), is not easily comprehensible. A close examination of the text, in light of the practice of States, shows that more than a simple dichotomy is involved. It seems necessary to distinguish between no less than four categories of self-defence: (i) individual self-defence individually exercised; (ii) individual self-defence collectively exercised; (iii) collective self-defence individually exercised; and (iv) collective self-defence collectively exercised.
(a) Individual Self-Defence Individually Exercised
786. The first category represents the most straightforward implementation of the right of self-defence, and it has been dealt with in Chapter 8: Arcadia perpetrates an armed attack against Utopia, and in response Utopia invokes self-defence. This is a one-on-one forcible encounter, and the right of individual self-defence is exercised individually.
(b) Individual Self-Defence Collectively Exercised
787. The second category relates to the situation where an armed attack is launched by the same aggressor (Arcadia), either simultaneously or consecutively, against several States (Utopia, Ruritania, etc.). Both Utopia and Ruritania are entitled to resort to measures of individual self-defence against Arcadia. These measures may be taken individually, each victim State declining any suggestion of close cooperation with the other. Utopia and Ruritania, while resisting armed attacks by the same aggressor (Arcadia), are not obliged to consolidate a united front. When recent relations between Utopia and Ruritania have been characterized by a deeply felt animosity, let alone a longstanding antagonism with historical roots, either country is apt to be opposed to the idea of recasting the political landscape, and it may elect to act on its own.
788. However, particularly when a large-scale invasion is in progress, States trying to resist aggression are disposed towards overlooking past grievances and forging a coalition, proceeding on the basis of the principle that ‘the enemy of my enemy is my friend’. The essence of a coalition is that its members marshal their combined resources and act jointly in effecting their respective rights of self-defence. It is sometimes argued that such a situation was envisaged by the authors of the Charter when they referred to ‘collective’ selfdefence.