The meaning of self-defence
494. In its 1996 Advisory Opinion on the Legality of the Threat or Use of Nuclear Weapons, the International Court of Justice said:
Furthermore, the Court cannot lose sight of the fundamental right of every State to survival, and thus its right to resort to self-defence, in accordance with Article 51 of the Charter, when its survival is at stake.
The implication is that the right of self-defence is engendered by, and embedded in, the fundamental right of States to survival. However, the Court itself acknowledged that ‘the very survival of a State would be at stake’ only ‘in an extreme circumstance of self-defence’ (see the full quotation, in its context, supra 462). Extreme circumstances of self-defence – when the very survival of a State is imperilled – do arise from time to time, but the exercise of self-defence is by no means confined to such catastrophic scenarios. The reality of self-defence in inter-State relations is much more prosaic: it transcends life-or-death existential crises and impinges on a host of commonplace situations involving the use of counter-force.
495. The essence of self-defence is self-help: under certain conditions set by international law, a State acting unilaterally – perhaps in association with other countries – may respond with lawful force to unlawful force (or, according to some, to the imminent threat of unlawful force). The reliance on self-help, as a remedy available to States when their rights are violated, is and always has been one of the hallmarks of international law. Self-help is a characteristic feature of all primitive legal systems, but in international law it has been honed to art form.