The Relationship Between Third-Party Countermeasures and the Security Council’s Chapter VII Powers: Enforcing Obligations Erga Omnes in International Law

Abstract: This thesis has examined the relationship between third-party countermeasures under the law of state responsibility and UN Security Council enforcement measures under Chapter VII of the UN Charter. Third-party countermeasures are a concept that refers to the use of countermeasures by a state other than the injured state in response to breaches of obligations erga omnes or erga omnes partes, providing states with ‘a necessary middle ground between war and words’ to enforce the obligations of concern to the international community as a whole. However, the right to take third-party countermeasures is a deeply divisive topic in the law of state responsibility. A significant source of this controversy relates to the uncertain relationship between third-party countermeasures and the Security Council’s enforcement powers under Chapter VII of the UN Charter. It has been suggested that recognising a regime of third-party countermeasures ‘would install a “do-it-yourself” sanctions system that would threaten the [collective] security system based on Chapter VII of the Charter of the United Nations’, undermining the institutional balance established thereunder. As state practice indicates with increasing clarity that the right to third-party countermeasures is emerging under customary international law, it is necessary to consider in further detail the legal position of such measures in relation to the Security Council’s mandate for the maintenance of international peace and security. It is submitted that the right of individual states to take third-party countermeasures is not precluded or subject to other limitations when taken in response to situations where the Security Council is either actively seized with a matter or taking enforcement action under Chapter VII of the UN Charter. In fact, in a number of instances, third-party countermeasures have been taken concurrently with Security Council enforcement measures without coming into conflict with or undermining the effective application of the latter. As such, the risks relating to the use of third-party countermeasures in relation to the Security Council do not appear to have materialised in practice. The uncertain relationship between third-party countermeasures and Security Council enforcement measures therefore appears to be mostly a theoretical or ideological problem without significant risks in practice.