A great part, then, of International Law is Roman Law, spread over Europe by a process exceedingly like that which, a few centuries earlier, had caused other portions of Roman Law to filter into the interstices of every European legal system. The Roman element in International Law belonged, however, to one special province of the Roman system, that which the Romans themselves called Natural Law or, by an alternative name, Jus Gentium. In a book published some years ago on ’Ancient Law’ I made this remark: ’Setting aside the Treaty Law of Nations, it is surprising how large a part of the system is made up of pure Roman law. Wherever there is a doctrine of the Roman jurisconsults affirmed by them to be in harmony with the Jus Gentium, the Publicists have found a reason for borrowing it, however plainly it may bear the marks of a distinctively Roman origin.’ I must observe, however, that the respect for natural law as the part of the Roman Law which had most Cairns on our reverence did not actually begin with the international lawyers. The habit of identifying the Roman law with the Law of Nature, for the purpose of giving it dignity, was of old date in Europe. When a clergyman or a lawyer of an early age wishes to quote the Roman Law in a country in which its authority was not recognised, or in a case to which Roman Law was not allowed to apply, he calls it ’Natural Law.’ When our Edward III laid a document before the Pope for the purpose of establishing his claim to the French throne, and of contending that the descendants of women may succeed to the property or throne of a male ancestor, he spoke of himself as arguing on Natural Law; though in point of fact the power of women to transmit rights of inheritance to their descendants was pure Roman Law of recent origin, and was not specially connected in any way with the Law of Nature.

But though the founders of the system which lies at the basis of the rules now regulating the concerns of states inter se were not the first to describe the Law of Nature and the Law of Nations, Jus Nature, Jus Gentium, as the most admirable, the most dignified portion of Roman Law, they speak of it with a precision and a confidence which were altogether new. They look upon it as perfectly determinable if the proper tests be applied, partly on the authority of express texts of Roman Law, partly by a process of inference from a great mass of recorded precedents. Its fitness for international purposes they regard as a discovery of their own, and some writers of their day speak of the system as the new science. No more doubt of its reality seems to have been entertained than (let us say) of the English common law by an English mediaeval lawyer. It is sometimes difficult to be quite sure how Grotius and his successors distinguished rules of the Law of Nature from religious rules prescribed by inspired writers. But that they did draw a distinction is plain. Grotius’s famous work, the ’De Jure Belli et Pacis,’ is in great part composed of examples supplied by the language and conduct of heathen statesmen, generals, and sovereigns, whom he could not have supposed to know anything of inspired teaching. If we assume him to have believed that the most humane and virtuous of the acts and opinions which he quotes were prompted by an instinct derived from a happier state of the human race, when it was still more directly shaped and guided by Divine authority, we should probably have got as near his conception as possible. As time has gone on, some parts of this basis of thought have proved to be no longer tenable. Grotius greatly overrated the extent of recorded history and, still more, the accuracy of the record. The very conception from which he started, the conception of a real and determinable Law of Nature, has not resisted the application of modern criticism. To each successive inquirer, the actual childhood of the human race looks less and less like the picture which the jurists of the seventeenth century formed of it. It was excessively inhuman in war; and it was before all things enamoured of legal technicality in peace. But nevertheless the system founded on an imaginary reconstruction of it more and more calmed the fury of angry belligerency, and supplied a framework to which more advanced principles of humanity and convenience easily adjusted themselves.

The effects of the ’De Jure Belli et Pacis,’ both in respect of its general influence and of the detailed propositions which it laid down, were exceedingly prompt and have proved extremely durable. At about the middle of his reign Louis XIV of France adopted two measures by which he was thought to have carried the severity of war to the furthest point. He devastated the Palatinate, expressly directing his officers to carry fire and sword into every corner of the province, and he issued a notice to the Dutch, with whom he was at war, that, as soon as the melting of the ice opened the canals, he would grant no more quarter to his Dutch enemies. The devastation of the Palatinate has become a proverb of savageness with all historians, though fifty years earlier it might at most have been passed as a measure of severity, or might even have been defended; but the proclamation to the Dutch called forth a burst of execration from all Europe, and the threat to refuse quarter was not acted upon. The book of Grotius was making itself felt, and the successors of Grotius assure us that it was his authority which deterred the French king and the French generals from the threatened outrage.

But there is other evidence of the respect paid to the details of his system. Among the most interesting legal products of our day are the Manuals of the usages of war which a great number of civilised states are now issuing to their officers in the field. The Manual prepared for the United States is the oldest of them, but most of them have followed the attempt to form a Code of Land War which was made at the Conference at Brussels in 1874, an attempt which miscarried principally through recollections of the course of the great Franco-German war in 1870-1871. There is very much that is remarkable in all this private codification, as I propose to show in one or two lectures which will follow; but perhaps the most singular feature of the Manuals is the number of rules adopted in them which have been literally borrowed from the ’De Jure Belli et Pacis,’ and specially from its third book. Remembering what Grotius himself says of the condition in which he found the law and usage of war when be began to write of it, and recalling what we learn from historical sources of the wars of succession and the wars of religion, we may well believe Vattel, the Swiss Jurist, a contemporary of the Seven Years’ War and of Frederick the Great, when he tells us that what struck him most in the wars of his day was their extreme gentleness; and of the standard of gentleness proper to be followed in war Vattel was a severe judge.

I here conclude this Introductory Lecture, but there still remain some points of principle which meet us on the threshold of International Law, and which cannot be dismissed absolutely in silence. In my next lecture I propose to consider the binding force of International Law, and with it a question of some gravity on which the judges of England and the legal authorities of the United States do not entertain absolutely identical opinions, and I will state the way in which I venture to think the various shades of difference can be got over. In the succeeding lectures I shall have to consider a few fundamental topics in the system before us, and I hope afterwards to give a sketch, which must be brief on account of the narrow limits of my course, on the law of war by sea and land; and finally I will endeavour to discharge a part of the duty imposed on me by Dr. Whewell’s directions, and to state what measures proposed in our day seem to me to tend to diminish the evils of war and to do something towards extinguishing it among nations.

Lecture II : Its Authority and Sanction

LECTURE II.
ITS AUTHORITY AND SANCTION.
In the latter portion of the last lecture I endeavoured to establish three propositions, which I hold to be extremely important to the intelligent study of International Law. The first of them was that the process by which International Law obtained authority in a great part of Europe was a late st age of the process by which the Roman Law had also obtained authority over very much the saline part of the world. Next, I said that this process had little or no analogy to what is now understood by legislation, but consisted in the reception of a body of doctrine in a mass by specially constituted or trained minds. Lastly, I contended that this doctrine, so spread over Europe, consisted mainly of that part of the Roman Law which the Romans themselves had called Jus Gentium or Jus Naturae -- Law of Nations, or Law of Nature; terms which had become practicably convertible.