The term has its roots in the *ius gentium* of Roman law, which, however, referred to the legal rules common to all peoples. International law in the modern sense, by contrast, refers to a body of law which primarily governs the conduct of states and international (inter-state) organisations, as well as the relations between them. Limited to specific areas of the international legal order – notably human rights and minority rights, as well as international tort law and international criminal law – individuals and non-governmental organisations (NGOs) have also been recognised as (partial) subjects of international law. Contrary to the conclusion suggested by the term in German, international law does not, strictly speaking, govern the legal relationships between‘peoples’, but rather, above all, the legal relationships between the states and confederations of states representing those peoples or nations.

English: public international law; French: droit international public; Russian: международное право (meždunarodnoe pravo); Polish: prawo międzynarodowe; Czech: mezinárodní právo; Spanish: derecho internacional público

‘Classical’ international law emerged in Europe at the end of the Reformation, the Counter-Reformation and the religious wars, with the ‘Peace of Westphalia’ signed in Münster and Osnabrück (1648). This treaty unreservedly recognised the sovereignty and equality of the states involved in the peace settlement, thereby putting an end to the Holy Roman Empire of the German Nation’s claims to supremacy and power, which were rooted in the medieval concept of a universal empire. A key element of sovereignty was the recognition of the right of states to decide freely on matters of war and peace (ius ad bellum). A tense pan-European system of states emerged, which was kept in balance by treaties under international law and the so-called ‘Concert’ of the major European powers.

The era of classical international law was succeeded by that of modern international law. Its symbol is the founding of the United Nations (1945). Modern international law is characterised, above all, by the prohibition on waging war at will. It was first established as a principle of international law by the Briand–Kellogg Pact (1928) and attained universal validity through the general prohibition on the use of force in the UN Charter (Article 2(4)).

The collapse of the Soviet Union, the dissolution of its hegemonic system and the end of the East-West conflict brought about by the pro-democracy revolutions in Eastern Europe (1989–1991) have ushered in a new phase in the development of international law. Its defining feature is that – despite many contradictions and limitations – states are, as a result, required to adhere more strictly than before to human rights and the standards of international humanitarian law. The sharp rise in humanitarian interventions (with or without a UN mandate) in cases of state collapse, genocide and mass crimes against humanity, as well as the establishment of a Permanent International Criminal Court based in The Hague (1998/2003), provide evidence of this. The global community – comprising states, international organisations, non-governmental organisations (NGOs), commercial enterprises and individuals – is therefore undergoing an accelerating process of consolidation and legalisation. This has led to the development of the international legal order, modelled on domestic and supranational arrangements, being interpreted as a process of ‘constitutionalisation’.

According to Article 38 of the Statute of the International Court of Justice (ICJ), the sources of international law are international treaty law, customary international law and ‘the general principles of law recognised by civilised nations’. The recognition of a norm by virtue of custom requires sufficient evidence of State practice, which must be underpinned by a general legal conviction and a corresponding intention to be legally bound. Treaties, resolutions and declarations by international bodies and national authorities, constitutional texts, decisions of international and national courts, and widely held scholarly opinions of recognised authorities in international law may provide evidence of this.

The international legal order and its norms comprise several dimensions and layers: universal international law constitutes the highest level. It is expressed in international treaties initiated by the UN, particularly those relating to human rights, and furthermore in customary international law applicable worldwide. Below this lies the level of regional international law (Article 52 of the UN Charter), namely that of Europe under the auspices of the Council of Europe (1949), the Americas in the form of the Organisation of American States (OAS, 1948), Africa in the form of the African Union (AU, 2000) and parts of Asia (Arab League, 1945; ASEAN, 1967; CIS, 1991).

The distinctive feature of the international legal order is that its principal subjects, the States, by virtue of their sovereign equality (Article 2(1) of the UN Charter), do not stand in a relationship of subordination to one another but rather in a relationship of coordination; consequently, they can, in principle, only form a common will and take decisions by mutual agreement through treaties. Unlike domestic law, international law cannot, as a general rule, be unilaterally enforced or implemented. The sanctions available to states in the event of conduct contrary to international law (reprisals, etc.) must, due to the prohibition on intervention, remain below the threshold of the use of force.

The International Court of Justice of the United Nations (ICJ, Art. 92 et seq. of the UN Charter) fits into this picture, as it corresponds more to an arbitral tribunal between states than to a ‘world court’. The ICJ’s jurisdiction is established only where the states referring a matter to it, including UN member states, have voluntarily submitted to its jurisdiction by means of a specific declaration.

Only the United Nations Security Council may, under certain conditions, unilaterally impose its will on states. For in the event of a threat to or breach of international peace (Article 39 of the UN Charter), it may take such measures as it deems necessary to maintain peace and, if necessary, may also use force against states or authorise individual states or groups of states to use force (Articles 41 and 42 of the UN Charter). However, this does not turn the Security Council into a world government. Whilst the general prohibition on the use of force applies to states, and the authority to use force is, in principle, reserved for the Security Council, the United Nations is by no means in possession of a universal monopoly on the use of force, as it does not have its own armed forces nor the actual power to enforce its will, even against resistance, if necessary. The United Nations’ powers of intervention are, in principle, limited by the right of states to decide at their own discretion on their ‘internal affairs’ (domestic affairs) – subject, of course, to compliance with their obligations under international law, for example in the field of human rights – as they see fit (Article 2(7) of the UN Charter).

The freedom of action enjoyed by subjects of international law when concluding international treaties is limited by peremptory norms of international law (ius cogens). According to Article 53 of the Vienna Convention on the Law of Treaties (23 May 1969), this refers to a norm ‘which is accepted and recognised by the international community as a whole as a norm from which no derogation is permitted and which can be modified only by a subsequent norm of general international law of the same legal nature’. A breach of a peremptory norm of international law renders the treaty null and void. It is generally accepted today that peremptory norms of international law are the fundamental principles of the UN Charter (Article 1; Art. 2), foremost among which is the prohibition of the use of force, including the prohibition of the annexation of another State’s territory; the human rights constituting the universal minimum standards under international law, namely the prohibition of torture and the prohibition of racial discrimination; the prohibition of genocide and crimes against humanity, the prohibition of slavery, and the right of peoples to self-determination.

Since the UN General Assembly’s Millennium Summit in 2000, the principle of national sovereignty (Article 2(1) of the UN Charter) has been undergoing a process of legal reinterpretation. Sovereignty is no longer regarded as authorising the state to take any political action it sees fit within its own borders. Rather, according to current understanding, the normative core of the principle is the state’s responsibility to protect the lives, liberty, property and assets of its citizens – the so-called ‘responsibility to protect’. If a state seriously breaches this obligation under international law, the international community is deemed to be entitled to impose sanctions on the state in question. It remains controversial, however, whether the UN Security Council alone is authorised to enforce the ‘responsibility to protect’, by force if necessary.

• Knut Ipsen: International Law. A Textbook, 6th, completely revised edition. Munich 2014.
• Juliane Kokott, Karl Doehring, Thomas Buergenthal: Fundamentals of International Law. 3rd, revised edition. Heidelberg 2003.
• Otto Luchterhandt: International Law versus Genocide: Significant Progress – Unresolved Problems. In: Journal of Genocide Research 9 (2008), Issue 2, pp. 10–67.
• Ignaz Seidl-Hohenfeldern, Torsten Stein: International Law. 10th, revised edition. Cologne et al. 2000 (Academia iuris).
• Theodor Schweisfurth: International Law. Tübingen 2006.
• Karl-Heinz Ziegler: History of International Law. An Academic Record. 2nd, revised and expanded edition. Munich 2007.

www.unric.org/de/voelkerrecht (Information provided by the United Nations Regional Information Centre for Western Europe)

Otto Luchterhandt: International Law. In: Online Encyclopaedia on the Culture and History of Germans in Eastern Europe, 2014. URL: ome-lexikon.uni-oldenburg.de/p32697 (as at 17 September 2021).