The right of self-defence against non-state actors is increasingly invoked and accepted in the practice of states. However, the recognition of this right must overcome a fundamental obstacle: that of explaining why the rights of the host state, in particular its right of territorial sovereignty, is not infringed by the self-defensive force used within its territory. In practice, states invoking self-defence against non-state actors rely on the involvement of the host state with those actors to justify the use of force in that state's territory. It is not clear, from a legal standpoint, how to rationalize the fact of involvement as a form of legal justification. For some, involvement amounts to attribution. For others, involvement is a form of complicity. For others still, involvement may entail a breach of the host state's due diligence obligation to protect the rights of other states in its territory. All of these solutions are deficient in some way, and have failed to receive general endorsement. This article considers whether there may be a different, as yet neglected, solution: self-defence as a circumstance precluding wrongfulness. The article shows that this is not a perfect solution either, since positive law remains uncertain on this point. Nevertheless, it is a solution that may provide a better normative framework for the development of the law of self-defence against non-state actors.

This article examines the law of self-defence as applied to non-state attacks in light of the coalition air strikes against ISIL in Syria. It critiques the two current interpretations of the law of self-defence – one based on attribution and the other on the ‘unable or unwilling’ test – for failing to address adequately the security threat posed by non-state actors or for not addressing convincingly the legal issues arising from the fact that the self-defence action unfolds on the territory of another state. For this reason, it proposes an alternative framework which combines the primary rule of self-defence to justify the use of defensive force against non-state actors, with the secondary rule of self-defence to excuse the incidental breach of the territorial state's sovereignty.

In view of the challenges frequently encountered in providing assistance to civilians in opposition-held territories, consideration is sometimes given to cross-border relief operations. Such operations raise numerous legal questions, including whose consent is required; what constitutes arbitrary withholding of consent; what the consequences of withholding of consent are, both for those wishing to provide assistance and for the parties withholding consent; and what alternatives exist for providing assistance in such circumstances.

For over three decades, it has been the International Law Commission's position that the circumstance of consent involves something other than the consent which, through the rule pacta sunt servanda, imparts objective force to international agreements. During the tenure of the second Special Rapporteur on the law of state responsibility, Roberto Ago, the Commission adopted the view that the former suspends the international obligations which are incumbent on states whereas the latter functions to create, modify, or extinguish the rules whence such obligations stem forth. However, as the result of the study carried out by its last Special Rapporteur, James Crawford, the Commission has now come to distinguish between the circumstance of consent defined as a justification for non-performance of subsisting obligations, and consent defined as a requirement for the application of obligations. In this contribution, it is argued that both analyses are problematic. The former gives succour to a mistaken view of the sources of international law. The latter is based on a misunderstanding of the primary-rule–secondary-rule terminology; it justifies itself by referring to an ill-conceived definition of the notion of peremptory norms, and no less importantly undermines the purposefully cumbersome mechanism envisaged in the 1969 Vienna Convention on the Law of Treaties for suspension of multilateral treaties as between certain of the contracting parties only.

García Amador, the first Special Rapporteur on the topic of state responsibility, was of the view that in international law, special circumstances denote situations of exemption from the secondary rule which attaches disadvantageous consequences to breach of obligation under any primary rule. By contrast, his successor, Roberto Ago, advanced the notion that the exceptional circumstances characterise situations of exemption from the obligations arising out of primary rules. In departure from both conceptions, James Crawford, the last Special Rapporteur on the law of state responsibility, submitted that it is only after having established that a certain course of behaviour is contrary to the terms of a prohibition that it becomes possible to enquire whether the actor had a justification for acting as he did. If affirmative, the conduct in question is to be regarded as conduct which neither conforms with the obligation nor constitutes a violation thereof. If negative, then the act amounts to an unjustified wrongdoing and accordingly forms the basis for the operation of the various disadvantageous consequences envisaged by the law of international responsibility. This contribution first examines the process of the development of the notion of exceptional circumstances in the edifice of the law of international responsibility ex delicto. It then shows that from the three competing conceptions, only that advanced by Ago proves capable of accurately accounting for the circumstances of consent, self-defence, and the legitimate application of a countermeasure.

This chapter examines the relevance of the principle of necessity to the international rules on the use of force. It claims that necessity has been the source of the international rules on the use of force which as independent titles manifest themselves in institutional as well as in customary forms. It also claims that the use of force constitutes a special regime of international law which is distinct from the law of state responsibility with which it however interacts.

This article studies the effects of invoking international necessity, to see whether it can be reconciled with an aspiring international rule of law. Any field of application in theory possible, the doctrine is here applied to uses of force, illustrated by humanitarian interventions, actions against international terrorism and the 2004 Construction of a Wall case. Relationships between circumstances precluding wrongfulness and the grounds for treaty termination is examined in light of international practice, studying necessity's impact on the stability of treaty regimes. The author concludes that international tribunals when applying necessity generally heed the rule of law, the stability of treaties and the elevation of overriding norms.

Necessity, if successfully invoked, is not perceived to alter substantive obligations. It cannot create a right to assume would-be illegal behaviour. As a result, necessity need not threaten international legal regime building, but may serve as a safety valve, allowing states to remain faithful to general norms, from which they are allowed to deviate only temporarily. In this manner, necessity can even contribute to the rule of law, thanks to its limited scope, constitutionalising emergency powers and subordinating them to pacta sunt servanda.