Traditionally, international law was divided into the law of war and the law of peace, with no intermediate stage between. When hostilities began, usually following a declaration of war, and non-parties to the conflict were held by the belligerents to be subject to the duties of, and they claimed the rights pertaining to, neutrals, war was recognised and the law of war came into operation. As with the situation under customary law, it is irrelevant whether the conflict is in accordance with the obligations of Hague Convention III, the Pact of Paris or the Charter of the United Nations. Even if the conflict does not amount to war in the legal sense of that term, there is nothing in international law, other than human rights conventions, preventing a country imposing restrictions upon the freedom of residents possessing adverse-party nationality.
The relations between a belligerent government and the adverse party's nationals are regulated partly by international and partly by national law. Civilians in the adverse party's territory are treated broadly speaking in accordance with the provisions of the national law, and while their freedom of movement may be restricted their treatment overall must be in accordance with Geneva Convention IV. If the capitulation relates to the surrender of an inhabited place, it may contain stipulations concerning the treatment of the civilian population. Conditions in a capitulation should relate only to the immediate purpose of effecting the surrender and not contain terms which would forbid the surrendered personnel from carrying arms in the future, for that is a political and not a military issue. Passports may be granted by a commander on his own authority or in accordance with his own military law.
Traditionally, for an armed conflict to warrant regulation by the international law of armed conflict, it was necessary for the situation to amount to a war, in other words, a contention between states through the medium of their armed forces. While the full panoply of the international law of armed conflict does not apply to non-international conflicts, to some extent non-international conflicts have come under the aegis of international law since 1977, with the adoption of Article 1 (4) of Protocol I. The first and only international agreement exclusively regulating the conduct of the parties in a non-international conflict is Protocol II additional to the 1949 Geneva Conventions. As to non-parties to the Conventions, in so far as the Conventions embody rules of customary law they will apply in any international armed conflict, as will all other rules of the customary law of armed conflict.
A non-international conflict has traditionally been one in which the governmental authorities of a state are opposed by groups within that state seeking to overthrow those authorities by force of arms. In accordance with the fundamental principle of customary international law concerning the independence of a sovereign authority, this type of conflict has traditionally been regarded as falling outside the ambit of international law. Apart from Article 3, common to the 1949 Conventions, the first major attempt to introduce international legal control of non-international conflicts by way of a statement of black-letter law is Protocol II, 1977, relating to the protection of victims of non-international conflicts. In non-international armed conflicts, as in those of an international character, civilians are to be protected against the dangers arising from the conflict.
In ancient times, as evidenced by the Laws of Manu, the Old Testament or the writings of Kautilya or San Tzu, there was no attempt to identify those who were entitled to be treated as combatants. It is only with the writers of the nineteenth century that either a clear definition of the rights of soldiers or the first use of the term 'combatants' is found. Irregular forces and resistance movements are protected only so long as they satisfy the normal requirements for recognition as combatants, in which case they are entitled if captured to be treated as prisoners of war. Until the adoption of Protocol I no attempt was made to discriminate among the members of an armed force on the basis of their nationality or the motives which lead them to join that force, whether those motives were ideological or mercenary.
This chapter introduces the study of the law of armed conflict by considering the nature and legality of war. The treatment of Napoleon served as a precedent for the policy adopted by the principal Allied and Associated Powers at the end of World War I when considering the treatment to be accorded to those responsible as authors of that war. A more definite attempt to render the war illegal is to be found in the Covenant of the League of Nations. The United States was not a member of the League, but by virtue of being among the victors in 1918 was an important power whose views could not be ignored. In 1946 the General Assembly at its first session adopted a resolution affirming 'the principles of international law recognised by the Charter of the Nuremberg Tribunal and the judgment of the Tribunal'.
Like other branches of international law, the law of armed conflict has no permanent means to secure its observance. Apart from the procedures established regarding prevention and supervision of breaches of the law, the surest guarantee of observance is compliance by a belligerent, even though reprisals or other retaliatory measures, such as the taking of hostages, are forbidden. Under the Geneva Conventions no party is able to absolve itself from liability, criminal or otherwise, for any grave breach of those Conventions. Protocol I introduced a new method of seeking to avoid breaches of the law or dealing with them when they occur. The greatest innovation effected by the Protocol in relation to supervision of its execution is the establishment of a permanent International Fact-Finding Commission which came into existence in 1992.
A civilian head of state who is the commander-in-chief of his nation's forces becomes a prisoner of war if he falls into enemy hands. Responsibility for the treatment of prisoners of war rests upon the detaining power, although they may be transferred to the custody of another party to the Convention and even, in some circumstances, to a neutral power. Broadly speaking, the duties of the Detaining Power are the concomitant of the rights of prisoners of war. In addition, however, there are duties directly imposed upon them and controlling their freedom of action. Prisoners of war are subject to the laws, regulations and orders of the Detaining Power, but must not be punished for any act which would not have been punishable if committed by a member of that Power's own forces.
In peacetime, when diplomatic relations are broken off between two countries, or when one is not represented in the territory of the other, they should follow some practice for representations. The normal practice is for the unrepresented one to nominate a third state acceptable to the recipient to represent its interests and protect its nationals in the recipient's territory. Each of the 1949 Conventions contains specific articles relating to the powers and functions of the Protecting Power, while Protocol I, 1977, has greatly improved the machinery for the appointment of a Protecting Power and increased its functions. Information concerning protected persons in the hands of an adverse party is transmitted to the state on whom they depend through the Protecting Power and the Central Prisoners of War or Central Information Agency. According to the Civilians Convention the Protecting Power is instrumental in protecting civilians, especially those in occupied territory.
The international law of armed conflict grants rights and imposes duties upon the non-participants, which are known as neutrals and the relevant legal regime as neutrality. Occasionally it is conceded that in certain circumstances a neutral may offer assistance to one of the belligerents on the basis of benevolent neutrality. A neutral has the right to permit belligerent troops to take refuge in its territory, but must intern them and prevent them from taking any further part in the conflict. If the neutral is a party to the Prisoners of War Convention, their treatment, if interned, must at least equal that required for prisoners of war. Subject to any regulations imposed by their government, neutral nationals may continue trading with either or both belligerents, but the articles involved are liable to seizure as prize.