Originally Posted by Dr Noel Cox
The scope of the law of war
Not every exercise of military force is lawful. Indeed, the tendency over the past few centuries has been to limit the freedom of sovereign states to levy war.(21) The instigation and conduct of war has since the very earliest times been subject to some degree of regulation or control. In the 13th century Thomas Aquinas wrote that, ‘in order that a war may be just three things are necessary. In the first place, the authority of the prince, by whose order the war is undertaken ... ‘(22) His second and third requirements for a just war, like those of his predecessor St Augustine, Bishop of Hippo, were a just cause, and right intent. Indeed, USA action could well be said to have qualified as a just war under Thomas Aquinas’ criteria, as it was waged by a sovereign state, in a just cause, and with right intent.(23)
However, the law of war has advanced much since St Thomas lived, and ironically, the UN Charter, designed to promote peace, enshrines a growing tendency to prohibit all wars not waged in self-defence,(24) though it does allow collective self-defence,(25) and the restoration of international peace.(26) This left little room for the ‘just war’, a concept which has nevertheless increasingly once again reared its head in the law of war.(27)
Traditionally the law of war was concerned with the regulation of warfare;(28) usually, though not exclusively, interstate warfare.(29) Additionally, since the 19th century there has been significant growth in the laws of humanity, or human rights.(30) It has been said that these two strands have joined.(31) There has been much concentration on humanitarian law, and especially the punishment of war criminals.(32) But the basic question of when it is lawful to start an offensive war had been examined relatively little.(33) For most purposes, the law of war may be divided into two parts: the legitimacy of the resort to force, and the rules governing the conduct of hostilities, often called jus ad bellum and jus in bello respectively. Both changed markedly in the course of the twentieth century.(34) It is with jus ad bellum with which this article is concerned.
The basic sources of the law of armed conflict are written and unwritten rules, treaties, agreements, and customary law. A treaty is an agreement between entities, both or all of which are subjects of international law possessed of international personality and treaty-making capacity.(35) All sovereign states enjoy the right to make treaties. Some self-governing colonies, protectorates, and international organisations have the capacity to enter into agreements, though their right to do so is usually limited.(36)
Custom is general state practice accepted as law. The elements of custom are a generalised repetition of similar acts by competent state authorities and a sentiment that such acts are juridically necessary to maintain and develop international relations.(37) The existence of custom, unlike treaty-law, depends upon general agreement, not unanimous agreement.(38)
It is now generally recognised that the law of armed conflict applies in all international armed conflicts, regardless of their legality.(39) They have now been extended to the modern phenomenon known as wars of national liberation. These revolutions are defined as armed conflicts in which peoples are fighting against colonial domination and alien occupation and against racist regimes in the exercise of their right of self-determination, as enshrined in the Charter of the UN and the Declaration on Principles of International Law concerning Friendly Relations and Co-operation among States in accordance with the Charter of the UN.(40)
There have long been efforts to codify the rules of war, generally those relating to the conduct of hostilities (jus in bello), but also those dealing with the legality of the use of force (jus ad bellum).(41) One early modern attempt was by Francis Lieber, whose Instructions for the Government of Armies of the United States in the Field, was promulgated by President Abraham Lincoln in 1863.(42) But articles of war, governing the conduct of national armies in the field, had been issued since early times, and reached their culmination in England in the 17th century.(43)
The first major international attempt at codification was the Hague Peace Conference in 1899, where a number of conventions on the law of war were adopted.(44) Then in 1907, another conference at The Hague revised the rules and made them more detailed. It also gave greater emphasis to the legality of the use of force – rather than being simply confined to questions of the legality of actions on the battlefield. The resulting Law of The Hague recognised that the total avoidance of war should be the ultimate goal. But it recognised that war is sometimes unavoidable, and was to this extent a legitimate means of settling disputes between nations.(45)
The Kellogg-Briand Pact 1928 (Pact of Paris) codified the customary law of war with respect to jus ad bellum. It was signed by 65 countries, including the USA,(46) who all thereby renounced aggressive war as an instrument of national policy.(47) In Article 1, ‘the high contracting parties condemn recourse to war for the solution of international controversies, and renounce it as an instrument of national policy in their relations with one another’.(48) The Treaty had the effect of outlawing war as an instrument of national policy (with respect to the signatories), and advanced the concept of aggressive war as being contrary to international law(49) – though it did not give rise to it – as this could be traced to Thomas Aquinas if not earlier.(50)
In 1945 and the years that followed, almost all nations signed the UN Charter, thereby promising to ‘refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the purposes of the UN’.(51) Hence, aggressive war, as such, had been eliminated from among the lawful means of conducting international relations. Yet, the use of armed force has not ceased.(52) International law has recognised this. In particular, the jus in bello part of the law of armed conflict applies not only to situations of declared war, but to any situation of international armed conflict and, to a more limited degree, armed conflicts which are not of an international character. Furthermore, armed force may be used pursuant to a decision or recommendation of the UN, in accordance with Article 42 of its Charter, and yet is not ‘war’ in the strict technical sense.