One distinguishes broadly between domestic, regional and (public and private) international law. Domestic law stems from domestic lawmakers and regulates the life of the citizens of a particular state. Regional law, such as European Union law or the law of regional human rights mechanisms, stems from regional intergovernmental institutions and addresses the governments and individuals of a particular geographical region or legal regime. Public international law is the subject of this chapter and addresses – in most general terms – relations involving states, intergovernmental organisations and non-state actors, which include today individuals, non-governmental organisations (NGOs) and private corporations. Private international law concerns conflicts of laws that may arise in cases where the domestic laws of different states could apply, for example in cases of cross-border e-commerce, marriages or liabilities.
Within public international law, a distinction is traditionally drawn between the law of peace and the law of war (humanitarian law). The law of peace regulates peaceful relations and includes such subject matters as international treaty law, the law of diplomatic and consular relations, international organisation law, the law of state responsibility, the law of the sea, the environment and outer space or international economic law.
International humanitarian law (IHL) is the law of armed conflicts (jus in bellum – the law applicable in war) and regulates the conduct of international and non-international hostilities. In times of war, the use of force, including the killing of human beings, is not prohibited. The legal regulation of armed conflicts goes back to the mid-nineteenth century and comprises a large body of customary rules and a series of important conventions and additional protocols to these conventions adopted primarily in The Hague and Geneva.
International humanitarian law regulates, among other things, the methods and means of warfare and the protection of certain categories of persons – for example, the sick and wounded, prisoners of war and civilians. More specific treaties prohibit the use of certain types of weapons (such as chemical or biological weapons, mines or cluster munitions) or the protection of cultural property during armed conflict. Much of the development and codification of this body of law is the merit of the International Committee of the Red Cross, founded in 1863 by Henry Dunant, which is a private humanitarian institution based in Geneva and forms part of the International Red Cross and Red Crescent Movement.
At the transitional points between the law of peace and the law of armed conflict lies the legal regulation of the resort to force (jus ad bellum – the law to engage in war) which concerns the conditions that need to be met to use force legally as, for example, in instances of self-defence (Article 51, UN Charter). More recently, scholars also speak of the regulation of the transition to peace after the end of armed conflicts (jus post-bellum – the law after war) which includes questions over how to end armed conflicts, transitional justice and post-war reconstruction.
The strict distinction between the law of peace and the law of armed conflict has been somewhat blurred with the rise of international human rights law and international criminal law. Human rights law builds on and develops fundamental principles of humanitarian law for the protection of individuals. On the other hand, human rights have considerably influenced the refinement of humanitarian rules for the protection of combatants and civilians. International criminal law has seen a rapid development after the end of the Cold War first with the establishment of the international criminal tribunals for the former Yugoslavia and Rwanda and then with the establishment of the International Criminal Court in 2002.