THE GLOBAL HISTORY OF INTERNATIONAL LAW

International law is the body of rules and principles that governs the conduct of states and, increasingly, of international organisations and individuals in their relations with one another. Unlike the law of any single state, it has no global legislature to enact it, no global police to enforce it and no court whose jurisdiction is automatic. It rests instead on the consent of states, expressed through the treaties they conclude and the customs they observe. How such a body of law came into being, and how it grew from scattered practices among neighbouring peoples into a dense network of institutions and obligations, is the subject of this article.

The history of international law is often told as a European story that begins with Hugo Grotius and the Peace of Westphalia and spreads outwards to the rest of the world. That account captures the origins of the particular system that became globally dominant, but it leaves out a great deal. Organised relations between distinct political communities, governed by recognised rules about treaties, envoys and the conduct of war, developed independently in many parts of the world, often long before they did in Europe. A fuller history sets the European tradition alongside the Sub-Anatolian, Indian, Islamic, Chinese and other traditions from which the present order also draws and attends to how that order came to be extended, often by force, to peoples who had legal traditions of their own.

Ancient Sub-Anatolian And Mediterranean Practice

Practices resembling international law existed in the earliest civilisations. The city-states of ancient Mesopotamia concluded treaties, defined boundaries and exchanged envoys. One of the earliest surviving international treaties is the agreement concluded in the thirteenth century before the common era between the Egyptian pharaoh Ramesses the Second and the Hittite king Hattusili the Third, which provided for peace, mutual defence and the return of fugitives; a copy of its text is displayed at the headquarters of the United Nations as a reminder of the antiquity of treaty-making.

In the classical Mediterranean, the Greek city-states developed conventions governing the conduct of war, the inviolability of heralds and the protection of sanctuaries, as well as systems of arbitration to settle disputes. The Roman jurists later developed the concept of the ius gentium, the law of nations, which referred to rules thought to be common to all peoples and discernible by reason. This was not international law in the modern sense, since it operated within the Roman legal order rather than between sovereign equals, but it bequeathed a vocabulary that later European writers would draw upon.

The Indian Tradition

The Indian subcontinent developed a sophisticated body of thought on relations between states well before the common era. The Arthashastra, a treatise on statecraft attributed to the minister Kautilya and composed in the centuries around 300 before the common era, set out a detailed theory of inter-state relations among the many kingdoms of the region. It described a system, sometimes called the mandala or circle of states, in which each ruler had to manage relations with neighbours, with the neighbours of neighbours and with potential allies and enemies, and it analysed treaties, alliances, neutrality and diplomacy in systematic terms.

Indian tradition also developed rules restraining the conduct of war. The Dharmaśāstra literature, including the text known as the Manusmṛti, laid down limits on what warriors might do: that those who had surrendered, the wounded and non-combatants should be spared, that certain weapons were forbidden and that envoys were not to be harmed. These were ethical and religious injunctions rather than treaties between equals, but they reflected a developed sense that warfare between political communities was subject to recognised constraints.

The Islamic Tradition

Among the most fully elaborated bodies of pre-modern thought on relations between political communities was the Islamic law of nations, known as siyar. From the eighth century of the common era, Muslim jurists developed detailed rules governing treaties, the treatment of envoys, the conduct of war, the protection of non-combatants and the obligations owed to those granted safe conduct. The jurist Muhammad al-Shaybani, who lived in the eighth and early ninth centuries, composed works on siyar so systematic that he is sometimes described as a founder of international law in his own tradition, comparable in standing to the role later assigned to Grotius in the European one.

This jurisprudence addressed many of the questions that international law still treats. It distinguished between binding and non-binding agreements, regulated the granting of guarantees of safety to foreign merchants and travellers, insisted on the observance of treaties once concluded and set limits on the killing of women, children, the elderly and others not engaged in fighting. It governed relations both with non-Muslim powers and among Muslim rulers, and was applied across the wide territories in which Islamic law held authority, showing that the systematic legal regulation of inter-state relations was by no means a European invention.

Chinese And East Asian Practice

In East Asia, the states of ancient China developed extensive inter-state practice during the Spring and Autumn and the Warring States periods, in the centuries before the region was unified under a single empire in the year 221 before the common era. Numerous rival states concluded treaties and alliances, held conferences, exchanged envoys and observed conventions governing diplomacy and war. Covenants sworn between states, often accompanied by ritual, were used to bind rulers to their undertakings, and a body of practice grew up around their negotiation and observance.

After unification, and through the long history of the Chinese empires that followed, relations with surrounding peoples were frequently ordered through what is often described as a tributary system, in which neighbouring rulers acknowledged the precedence of the Chinese emperor and exchanged missions according to elaborate protocol. Organised around hierarchy and ritual rather than the equality of sovereigns, this was nonetheless a durable framework for managing relations between distinct political communities across a vast region over many centuries.

The European Natural-Law Tradition

The particular tradition that would eventually furnish the vocabulary of the modern global order took shape in Europe, and its intellectual foundations lay in natural law, a set of principles held to be binding on all human beings by virtue of reason rather than by the command of any ruler. The Spanish theologians of the sixteenth century, writing in the period of European expansion into the Americas, were among the first to apply this tradition systematically to relations between peoples.

The Dominican theologian Francisco de Vitoria, lecturing at the University of Salamanca, examined the rights and duties arising from the encounter between the Spanish crown and the indigenous peoples of the Americas. He argued that those peoples possessed genuine rights, that they could not be deprived of their lands merely on grounds of unbelief and that relations between all peoples were governed by a law of nations binding on rulers everywhere.

The Jesuit philosopher Francisco Suárez later developed the idea that the law of nations occupied a distinct place between natural law and the civil law of particular states. It is notable that this European tradition was prompted in part by the encounter with non-European peoples, and that the same arguments which affirmed their rights were also used to justify the conditions under which Europeans might trade among them, travel through their lands and wage war upon them.

Hugo Grotius And The Law Of War And Peace

The figure most often described in the European account as the father of international law is the Dutch jurist Hugo Grotius. His major work, De Jure Belli ac Pacis, meaning On the Law of War and Peace, was published in 1625, during the Thirty Years’ War that was then devastating central Europe. Confronted with a conflict of great destructiveness, Grotius sought to show that even war was subject to law, and that states, like individuals, were bound by rules they could not rightly ignore.

He argued that a law of nations could be derived from reason and from the agreed practice of states, and that it would remain binding even if, as he put it in a celebrated phrase, one were to grant that God did not exist. By treating the law of nations as a coherent system that could be studied systematically, Grotius gave the subject a form that later European jurists could build upon, addressing when war could justly be undertaken, how it ought to be conducted and how peace was to be restored.

Westphalia And The System Of Sovereign States

The political framework within which the modern system operates is conventionally traced to the Peace of Westphalia, the treaties concluded in 1648 that ended the Thirty Years’ War. The settlement is associated, in the standard account, with the principle of state sovereignty: the idea that each state exercises supreme authority within its own territory and acknowledges no superior outside it.

On this understanding, the international order came to be conceived as a society of sovereign states, formally equal to one another, each free to govern its internal affairs without external interference. Whether the treaties of 1648 themselves established all that is later attributed to them has been questioned by historians, and the tidy story of a single founding moment is now treated with caution. The Westphalian model nonetheless became the organising idea of the European tradition, and it was this image of a world ordered into territorial sovereign states that would later be projected across the globe.

The Positivist Turn And The Standard Of Civilisation

As the European system matured, the basis on which its law was understood began to shift. The earlier writers had grounded the law of nations in natural law, in principles of reason valid everywhere. From the eighteenth century onwards, a growing number of jurists came to emphasise instead the actual practice and consent of states as the true source of their obligations. This approach, called positivism, located the law in what states had agreed to and what they did. The Swiss jurist Emer de Vattel occupies a transitional place; his treatise Le Droit des gens, meaning The Law of Nations, published in 1758, applied the language of natural law to states conceived as free and independent persons and was widely read by diplomats.

This positivist turn had a consequence that bears directly on the global history of the subject. As the law came to be defined by the practice of a particular group of states, jurists of the nineteenth century increasingly held that its full protections applied only among those they regarded as civilised nations, a category confined largely to the states of Europe and of European settlement.

Other peoples, including those of long-established traditions in Asia and Africa, were admitted only partially or on unequal terms, if at all. This so-called standard of civilisation was used to justify unequal treaties, the extension of European jurisdiction over non-European populations and the acquisition of their territories. The history of international law in this period is therefore inseparable from the history of colonialism, a connection that complicates any account of the law as a straightforward instrument of order and peace.

Codification, The Hague And The League Of Nations

The nineteenth century brought a sustained effort to set down the rules in written form, a process known as codification. States concluded multilateral treaties on subjects ranging from the navigation of rivers to the treatment of the wounded in war; the first of the Geneva Conventions, concluded in 1864, marked the beginning of modern international humanitarian law. The peace conferences held at The Hague in 1899 and 1907 produced conventions on the laws of war and on the peaceful settlement of disputes, and established the Permanent Court of Arbitration.

After the First World War came the League of Nations, established in 1920 as the first general international organisation devoted to maintaining peace through collective action, and the Permanent Court of International Justice, the first standing court with general jurisdiction to decide disputes between states. The League failed to prevent a second descent into general war, but it established institutional forms, an assembly, a council and a standing court, that would be revived after the next conflict.

The United Nations And Modern International Law

The most consequential development followed the Second World War. In 1945, representatives of fifty states meeting at San Francisco adopted the Charter of the United Nations, establishing an organisation intended to maintain international peace and security, to develop friendly relations among nations and to promote cooperation in solving international problems. The Charter prohibited the threat or use of force by states against one another, subject to defined exceptions, and vested in the Security Council the primary responsibility for maintaining peace.

It also established the International Court of Justice as the principal judicial organ of the United Nations, whose Statute set out the sources of international law the court would apply: international conventions, international custom, the general principles of law recognised by nations and, as a subsidiary means, the writings of jurists and the decisions of courts.

The post-war period also saw the law expand far beyond the relations of states and beyond its European origins. The trials conducted at Nuremberg established that individuals could be held criminally responsible under international law for grave offences, including war crimes and crimes against humanity. The Universal Declaration of Human Rights, adopted by the General Assembly in 1948, inaugurated a body of human rights law addressing the treatment of individuals by their own states.

Above all, decolonisation transformed the discipline: as a large number of newly independent states in Asia, Africa and elsewhere joined the international community, they took part in making the law and pressed for principles, such as the sovereign equality of states, the self-determination of peoples and permanent sovereignty over natural resources, that reshaped it. Specialised legal frameworks developed to govern trade, the law of the sea, the environment and many other fields, and an International Criminal Court was established by treaty in 1998 to try individuals for the gravest international crimes.

Conclusion

The history of international law is wider than the European account that long stood for the whole. Systematic rules governing treaties, diplomacy and the conduct of war developed in the ancient Sub-Anatolia, in India, in the Islamic world, in China and elsewhere, often independently and often earlier than in Europe.

The European tradition, given lasting form by writers such as Hugo Grotius and framed within the system of sovereign states associated with the Peace of Westphalia, was one tradition among several; what distinguished it was that, through European expansion and colonial power, its forms came to be extended across the globe, at times by excluding or subordinating the very peoples who possessed legal traditions of their own.

The institutions of the present order, above all the United Nations and the International Court of Justice, were built in the twentieth century, and through decolonisation that order came to include the whole community of states in its making. International law remains a law without a sovereign above it, dependent on the consent and conduct of states for its force, constructed from many sources and over many centuries.