The relationship between jus ad bellum and jus in bello is both fascinating (because it challenges some fundamental concepts of international humanitarian law) and of crucial importance (because current "attacks" against the absolute distinction between these two branches of international law might well jeopardize the fate of innumerable victims of armed conflicts).
In this short contribution we will successively:
* offer some basic definitions and examine the origin of the two concepts:
* discuss the basis of the distinction;
* present the current challenges to the distinction: and
* discuss the reasons why, in our view, the distinction must be maintained.
BASIC DEFINITIONS AND ORIGIN OF THE TWO CONCEPTS
Jus ad bellum can be defined as the rules regulating the resort to armed force. As long as war was considered as "just another means of settling disputes," jus ad bellum was quite developed. With the gradual prohibition of the resort to armed force, which culminated in the adoption of the UN Charter, jus ad bellum became increasingly limited. As of today, it is limited in practice to self-defense (Article 51 of the Charter) and collective security operations (Chapter VII of the Charter).
Jus in bello defines what is legal in armed conflicts. More commonly referred to as international humanitarian law (IHL), it aims in particular at:
* sparing those not directly involved in hostilities, and
* limiting the violence to the amount necessary to achieve the aim of the conflict.
Without entering into historical details, (1) it should be mentioned that the concepts of jus ad bellum and jus in bello developed as a result of the gradual obsolescence of the just war theory initially elaborated by Grotius. (2) From the mid-nineteen century on, jus ad bellum and jus in bello developed as separate and distinct branches of international law.
From a quantitative perspective their respective development followed an opposite course: while jus ad bellum was gradually reduced to the two exceptions spelled out in the UN Charter, jus in hello was developed into hundreds of conventional and customary rules.
BASIS OF THE DISTINCTION
The idea that both branches operate autonomously is firmly rooted in 1) the legal literature, 2) state practice, 3) the jurisprudence of national and international courts, and 4) several treaties. For Greenwood, both branches "seldom sat happily together" and they "can and should be regarded as distinct from another." (3)