(p. 3)  Introduction

‘Then felt I like some watcher in the skies

When a new planet swims into his ken…’


1.  Development of the Law of Nations

The law of nations, now known as (public) international law,2 developed out of the tradition of the late medieval ius gentium.3 Through an influential series of writers— Vitoria,4 Gentili,5 Grotius,6 Pufendorf,7 Wolff,8 Vattel,9and others—it came to be seen as a specialized body of legal thinking about the relations between rulers, reflective of (p. 4) custom and practice in such matters as treaty-making, the status of ambassadors, the use of the oceans, and the modalities of warfare. It was not continuous with the ius gentium of the Romans, but the thirteenth-century rediscovery of Roman or civil law by figures such as Thomas Aquinas10 reinforced the idea that law could structure or at least moderate the relations between kingdoms, principalities, and republics.11The Thomist conceptualization of such relations owed much to the notion of the ‘just war’ that was later to preoccupy Grotius and others. At that time, international law—if the term was even applicable—was essentially a moral question (resulting in the elevation of the ‘just war’ to a matter of Christian doctrine); but it was engaged with issues familiar to a modern practitioner, such as territorial claims, treaties, the right of legation, and related matters.12 A signal development hinting at advances yet to come was that war was seen as the prerogative of the sovereign:

For it is not the business of a private individual to declare war, because he can seek for redress of his rights from the tribunal of his superior. Moreover it is not the business of a private individual to summon together the people, which has to be done in wartime. And as the care of the common weal is committed to those who are in authority, it is their business to watch over the common weal of the city, kingdom or province subject to them.13

In terms of intellectual history, international law was thus European in origin, although the Europe in question was large, extending to the whole Mediterranean, to Russia and the Near East; thence international law travelled with the colonizers to the Americas, to Asia, to Africa and eventually to Oceania.14 At this time Europe was not chauvinistic in defining membership of the international system.15 For example, the Ottoman Empire was accepted as a valid participant as early as 1649.16

In the Far East, a number of states such as Siam/Thailand, China, and Japan survived the colonial onslaught and continued to assert their independence, as demonstrated by Macartney’s embassy to China in 1792 and his acid reception by the Qianlong Emperor.17 By the mid-nineteenth century China had been largely cowed (p. 5) by the use of gunboat diplomacy, leading to the Treaties of Beijing in 1860.18 Japan, by contrast, engaged in a controlled opening to the west, with British naval advisers and an early translation of Wheaton’s International Law.19 A few Asian nations were able to maintain their autonomy, either because it was convenient for the colonial powers (as in the case of Siam/Thailand) or because the state succeeded in internal modernizing (as in the case of Japan, whose navy crushed Russia’s at the battle of Tsushima in 1905). Similarly, Ethiopia was able to maintain its independence at the expense of Italy following the latter’s defeat at the battle of Adowa in 1896. The remainder of the African continent, however, was subjugated: following the Berlin Conference of 1884 and the ‘Scramble for Africa’20 it was divided between Great Britain, France, Belgium, Germany, Spain, Portugal, and Italy to create a political landscape that would last until after the Second World War.21

By this stage, the ‘modern structure’ of the law of nations was recognizably in place. The system of diplomatic relations, recognition, international organizations, treaties, and customary international law had taken on essentially modern contours. At the same time, colonialism had reshaped the world in a Eurocentric image. By the 1920s, the number of states in the world had been reduced to some 64, of which 16 were former Spanish and Portuguese colonies in South and Central America. Of the non-European nations, only seven—Ethiopia, Liberia, the Ottoman Empire (Turkey), Thailand, China, Japan, and Afghanistan—had managed to retain independence without formal qualification of their sovereignty.

Perhaps as a concomitant of this reduction, sovereignty was assigned unique value in the international sphere. By the 1920s, it was widely thought that international law was entirely dependent on the consent—express or implied—of states,22 and was applicable to states alone: ‘Since the Law of Nations is based on the common consent of individual States, and not of individual human beings, States solely and exclusively are the subjects of International Law’.23 But the influence of earlier eras was not entirely expunged. Even at this point in time—the crest of the positivist wave—the Permanent Court of International Justice had indicated that rights under international law could be conferred on individuals.24

(p. 6) At around this time, international legal personality gained an added dimension with the emergence of international organizations. In the nineteenth century states moved from the bilateral treaty and reliance on diplomatic contact to other forms of co-operation. The Congress of Vienna (1814–15) heralded an era of international conferences and multilateral treaties: later there appeared river commissions such as the European Commission of the Danube (1856) and administrative unions such as the International Telegraph Union (1865). After 1919 the League of Nations and then the United Nations provided a more developed attempt at universal peacekeeping arrangements, and many specialized institutions concerned with technical, economic, and social co-operation were established. Permanent organizations with executive and administrative organs paralleled but did not completely replace the system of ad hoc diplomacy and conferences.25

Over the course of the twentieth century, international law underwent a profound process of expansion. Developments included, inter alia, the creation of international organizations of universal membership with treaty-making powers (see chapter 7), a detailed elaboration of the law of the sea (see chapters 11–13), the establishment of permanent bodies (or at least permanently available institutions) for the settlement of international disputes, including ‘mixed’ disputes between states and private parties (see chapter 32), the prohibition on the use of force by states (see chapter 33); the emergence of various sub-disciplines or specialist areas of work and study; notably, human rights (see chapter 29), international environmental law (see chapters 1415), international economic law,26 international criminal law (see chapter 30), and progress towards the codification of international law, principally through the work of the International Law Commission.27

2.  International Law as Law

At an elementary level, the normative system of international law is derived from four sources, enumerated in Article 38(1) of the Statute of the International Court of Justice: (1) treaties; (2) customary international law; (3) general principles of law; and (4) ‘judicial decisions and the teachings of the most highly qualified publicists of the various nations, as a subsidiary means for the determination of rules of law’.28 But (p. 7) these, important in their own right, tell us little about the wider intellectual history of the field or its normative underpinnings.

(A)  Natural Law Origins

The early development of international law saw its gradual separation from natural law, a process spurred on by the Reformation and the wars of religion, notably the Thirty Years War which ended with the Peace of Westphalia (1648). Natural law as a school of thought had emerged from the philosophical traditions of Roman law and the Roman Church, which conceived of a universal ius naturale (natural law properly speaking) of which the ius gentium (the law of peoples) was a subset.29 Natural law, thus conceived, was universal; this was the background from which emerged Vitoria, Grotius, and other early theorists. Their contribution, willingly or not, was the separation of the ius gentium from the ius naturale and its modulation into a law of nations, which applied specifically to the rulers of states. This was particularly evident in the work of Grotius, who depicted international law as the gradual development of universal principles of justice which could be deciphered through human agency (independent of received religion):

But as the Laws of each State respect the Benefit of that State; so amongst all or most States there might be, and in Fact there are, some Laws agreed on by common Consent, which respect the Advantage not of one Body in particular, but of all in general. And this is what is called the Law of Nations, when used in Distinction to the Law of Nature.…

Let it be granted then, that Laws must be silent in the midst of Arms, provided they are only those Laws that are Civil and Judicial, and proper for Times of Peace; but not those that are of perpetual Obligation, and are equally suited to all Times. For it was very well said…That between Enemies, Written, that is, Civil Laws, are of no Force, but Unwritten are, that is, those which Nature dictates, or the Consent of Nations has instituted.…[T]here are some Things, which it would be unlawful to practise even against an Enemy.30

Thus understood, the law of nations was a system of norms whether derived from a universally applicable, ‘natural’ morality or attested by ‘the Consent of Nations’. But over time, thinking on the subject became progressively more concerned with a limited agenda of legal issues external to the state, as can be seen from a side-by-side comparison of Grotius’ De iure belli ac pacis (1625) and Vattel’s Le Droit des gens (1758). The bridge between the two was Wolff, who attempted a description of the ius gentium according to scientific principles.31 Wolff argued that collective society could (p. 8) not be promoted unless states formed a universal political entity, a ‘supreme state’ from which would proceed the law of nations:32

[A]ll the nations scattered throughout the whole world cannot assemble together, as is self-evident, that must be taken to be the will of all nations which they are bound to agree upon, if following the leadership of nature they use right reason. Hence it is plain, because it has to be admitted, that what has been approved by the more civilized nations is the law of nations.33

Wolff was the progenitor of Vattel’s Le Droit des gens, which could claim to be the first international law textbook.34 But Vattel’s text was at odds with many of Wolff ’s conclusions, most notably with the concept of the ‘supreme state’, preferring instead to see the (European) state system as a collective capable of acting in the common interest.35 Thus Vattel asserted that the continent formed…

a political system in which the Nations inhabiting this part of the world are bound by their relations and various interests into a single body. It is no longer, as in former times, a confused heap of detached parts, each of which had little concern for the lot of the others, and rarely troubled itself over which did not immediately affect it. The constant attention of sovereigns to all that goes on, the custom of resident ministers, the continual negotiations that take place, make of modern Europe a sort of Republic, whose members—each independent but all bound together by a common interest—unite for the maintenance of order and the preservation of liberty. Hence arose that famous scheme of the political balance, or the equilibrium of power.36

But greater minds than Vattel’s were at play. Immanuel Kant (1724–1809)37 sought to re-characterize the binding character of international law, proposing an international federation of republican states ( foedus pacificum)—along substantially similar lines to Wolff ’s ‘supreme state’38 —backed by coercive rules, as the only method by which a secure and lasting peace could be achieved:

There is only one rational way in which states coexisting with other states can emerge from the lawless condition of pure warfare. Just like individual men, they must renounce their savage and lawless freedom, adapt themselves to public coercive laws, and thus form an international state (civitas gentium), which would necessarily continue to grow until it (p. 9) embraced all the peoples of the earth. But since this is not the will of the nations, according to their present conception of international right…the positive idea of a world republic cannot be realised. If all is not to be lost, this can at best find a negative substitute in the shape of an enduring and gradually expanding federation likely to prevent war. The latter may check the current of man’s inclination to defy the law and antagonise his fellows, although there will always be a risk of it bursting forth anew.39

(B)  From Positivism to the Present Day

The early modern period also saw the emergence of ‘sovereign’ states from the claims of Empire, secular or religious. States emerged as material, independent entities and international law was one of the ways they developed of managing their relations. The apparent paradox of how law could operate between sovereigns is resolved by the priority given to consent in the formation of legal obligation and the role of co-operation in interstate affairs—combined with the insight that sovereignty includes the capacity to make commitments not merely temporary in character.40 Indeed the law itself begins to say what it takes to become a state and what, as a matter of law, it means to be a state.

Since the law of nations developed within a system wholly lacking in other institutions, international law is highly state-centric, a position reinforced from the early nineteenth century by the development and subsequent dominance of positivism as an account of law and legal obligation. Applied to jurisprudence, positivism was distinguished by the notion that only positive law—that is, law which had in some form been enacted or made by authority—could be considered true law. International law, which could only with difficulty be seen to be made—and then in a diffuse way—was caught up in this.

Positivism saw the law as a creation of power, a command of a sovereign enforced by a sanction. International law was not law above states, but law between states, enforceable, short of war, by way of moral opprobrium or by reciprocal denial of benefits. Indeed according to some positivists, notably John Austin (1790–1859), international law was only ‘law improperly so called’.41 In this sense, Austin conjectured:

[T]he law obtaining between nations is not positive law: for every positive law is set by a given sovereign to a person or persons in a state of subjugation to its author…[T]he law obtaining between nations is law (improperly so called) set by general opinion. The duties which it imposes are enforced by moral sanctions: by fear on the part of nations, or by fear on the part of sovereigns, of provoking general hostility, and incurring its probable evils, in case they shall violate maxims generally received and objected.42

Austin’s attitude to international law arose from its not complying with his positivist axiom: in the international system there was no sovereign, thus no command, and(p. 10) sanctions were decentralized and sporadic. This was an extreme position, not inherent in positivism as such but in the dogma of a single sovereign as the fount of all law. Austin’s friend and intellectual predecessor—Jeremy Bentham (1748–1832)—had no such issue with international law, principally because he thought that national sovereigns, just as they could proclaim laws for the benefit of their own communities, could also together promulgate international law: they were not disabled from collective action.43 Bentham, unlike Austin, also believed that a real law might be enforced by a religious or moral sanction:

When a foreign state stands engaged by an express covenant to take such a part in the enforcement of such a law as that in question, this is one of the cases in which a foreign state is said to stand with reference to such law in the capacity of a guarantee. Of a covenant of this sort many examples are to be met with in the history of international jurisprudence.44

A more refined version of positivist legal theory was elaborated by HLA Hart(1907–92). Drawing on Kelsen, Hart distinguished three categories of rules: (a) primary rules, concerning human action and interaction; (b) secondary rules (rules of adjudication, enforcement, and change) which underpin and operate in relation to the primary rules; and (c) the master ‘rule of recognition’, which enables the observer to identify the components of the system and to treat them as legal. It was the internal attitude, mainly of the officials, those responsible for the application of the secondary rules, which marked the system as legal and not merely a set of social rules. What mattered was not their acceptance of primary rules but their acceptance of the system by which those rules were generated and applied: it was the combination of primary and secondary rules which was the essence of law.45

Measured by this more complex standard, Hart saw international law as a marginal form, possessing some but not all the characteristics of a developed legal system and then only imperfectly.46 It had only rudimentary institutions of adjudication, enforcement, and change—no courts of compulsory jurisdiction, no legislature, a frail internal attitude on the part of officials: ‘no other social rules are so close to municipal law as international law’,47 but social rules they remained.

This position was the subject of critical scrutiny by Brownlie,48 who argued that whatever the theoretical overlay of law/not law imposed by Hart (and positivists in general), the reality of international law told a different story:

The lack of compulsory jurisdiction and a legislature is regarded by Hart not as the special feature of a system which operates in conditions of a certain kind, but as the marks of an outcast, of a butterfly which is not wanted for a pre-determined collection. Yet…the stability of international relations compares quite well with internal law, given the grand (p. 11) total of municipal systems ruptured by civil strife since 1945. And whilst it may be said that international law lacks secondary rules, this matters less if one accepts the view that secondary rules do not play such a decisive role in maintaining the more basic forms of legality in municipal systems.49

(C)  The Basis of Obligation

In fact there are many examples of public order systems which lack an identifiable sovereign but manage to function—ranging from the customary laws of indigenous societies to the law of the European Union. The classification of a system as legal does not predetermine its effectiveness: witness various national law systems in greater or lesser disarray. The question is whether the rules, traditions and institutions of a given system enjoy at least some salience within the relevant society, meet its social needs, and are applied through techniques and methods recognizably legal—as distinct from mere manifestations of unregulated force. There is no reason to deny to such systems the classification of being legal—recognizing however that this leaves many questions open.

During the twentieth century, understanding of international law has been further articulated through sociological theories,50 as well as, latterly, by the resurgence of a more rigorous and pragmatic natural law approach.51 In particular, John Finnis has defended the idea of an international law—particularly customary international law—able to emerge without being made by anyone with authority to make it, and without the benefit of Hart’s secondary rules for the authorized generation and alteration of rules:

[A]lthough there are direct ‘moral’ arguments of justice for recognizing customs as authoritative…the general authoritativeness of custom depends upon the fact that custom-formation has been adopted by the international community as an appropriate method of rule creation. For, given this fact, recognition of the authoritativeness of particular customs affords all states an opportunity of furthering the common good of the international community by solving interaction and co-ordination problems otherwise insoluble. And this opportunity is the root of all legal authority, whether it be the authority of rulers or (as here) of rules.52

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