Introduction

This work addresses the development and current content of necessity and proportionality in the law on the use of force (ius ad bellum) and the law of armed conflict (ius in bello) or international humanitarian law (IHL). Before turning to a detailed consideration of the history and the modern content of necessity and proportionality in these two regimes, this first chapter provides an overview of the evolution of these twin concepts as part of the attempt by States through the development of legal norms to restrict the circumstances in which States can resort to force and, where these restraints fail, to place limits on the manner in which ensuing hostilities are conducted.

Necessity and proportionality are concepts that over the years have had differing applications in international law in the context of both pacific and non-pacific actions of States. Today, for example, a state of necessity may be invoked by a State as a defence to a breach of an obligation imposed by international law. Currently, the practical relevance of the doctrine of necessity in the context of the forceful actions of States is largely limited to its operation in ius ad bellum. In that regime, necessity determines whether the situation warrants the use of armed force. As for IHL, the idea of necessity is traditionally regarded as a fundamental concept within that system. IHL is commonly described as a balance between the demands of military necessity and considerations of humanity.