The Distinction and Relationship between Jus ad Bellum and Jus in Bello

Abstract

1. This book is based on the author's doctoral thesis, completed at the University of Cambridge. It deals with the crucial tension and mutual support between the rules on the legality of the use of force (jus ad bellum) and the (humanitarian) rules applicable when force is used (jus in bello). The separation between the two branches is essential for the protection of all those affected by armed conflicts and it is, at least in theory, no longer controversial. Its humanitarian importance and theoretical background are fairly described by the author. He also stresses—and this has rarely been done before—how the two branches complement and reinforce each other, fill each other's gaps and, thus, improve the situation for all those affected by armed conflicts. The book analyses the relationship between the two branches, arguing that it is governed by three principles: first, separation between them; second, equal application of international humanitarian law (IHL) to the conflicting parties; and, third, concurrent application of both branches during an armed conflict (thus overcoming the older conception that jus ad bellum applies until a conflict breaks out, which is then regulated only by jus in bello). This analysis is then applied to a great variety of situations and questions arising in contemporary practice.