After the conflicts of the barbaric kingdoms which followed the dissolution of the Western Empire were ended by the predominance of the Frankish monarchy, the world believed that the Pax Romana was to be restored in Europe by the hand of Charles the Great; but the disruptive forces were destined to prevail once more, and the Holy Roman Empire never succeeded in reviving the power of ancient Rome. And thus the dream of a universal monarchy, of a central authority able to preside over kings and princes, adjusting their difficulties, and preserving the peace between them, was at last proved futile.
In each of the great national monarchies that had already risen or were still rising on the ruins of imperial dominion, particularly in France, England, Holland, and the States of Germany, a continuous internal conflict over questions of religion complicated the bitterness and destructiveness of foreign wars until Europe was reorganized by the Peace of Westphalia, in 1648.
It was in the midst of these wars that Grotius was born. He saw his own country rising from a baptism of blood and all Europe rent and torn by the awful struggle of the Thirty Years' War, in the midst of which his great work was written and to whose conclusion it served as a guide and inspiration. The Empire, dismembered, had been reduced to almost complete impotence, the Church had been disrupted, and no international authority was anywhere visible. Amid the general wreck of institutions Grotius sought for light and guidance in great principles. Looking about him at the general havoc which war had made, the nations hostile, the faith of ages shattered, the passions of men destroying the commonwealths which nourished them, he saw that Europe possessed but one common bond, one vestige of its former unity,—the human mind. To this he made appeal and upon its deepest convictions he sought to plant the Law of Nations.
II. The Predecessors of Grotius.
It is historically accurate to say, that, until formulated by Grotius, Europe possessed no system of international law. Others had preceded him in touching upon certain aspects of the rights and duties of nations, but none had produced a system comparable to his.
The earliest attempt to formulate recognized international customs was the formation of the early maritime codes, rendered necessary by the expansion of mediæval commerce from the end of the eleventh to the end of the sixteenth century, such as the "Jugemens d' Oléron," adopted by the merchants of France, England, and Spain, and reissued under other names for the merchants of The Netherlands and the Baltic. "The Consolato del Mare," a more elaborate compilation, was made, apparently at Barcelona, about the middle of the fourteenth century, and accepted generally by the traders of the chief maritime powers. It was in the cradle of commerce, therefore, that international law awoke to consciousness.
As the Church was often intrusted with the task of pacification, it is but natural to look among her representatives for the earliest writers on the laws of international relations. It is, in fact, among the theological moralists that we find the first students of this subject. As early as 1564, a Spanish theologian, Vasquez, conceived of a group of free states with reciprocal rights regulated by jus naturale et gentium, without regard to a world-power, either imperial or ecclesiastical. In 1612, Saurez pointed out that a kind of customary law had arisen from the usages of nations, and distinctly described a society of interdependent states bound by fundamental principles of justice.
At the close of the fifteenth and the beginning of the sixteenth centuries, a series of circumstances arose necessitating the extension of jurisprudence beyond its ancient boundaries, and thus tending to produce a group of international jurists. Among the juristic writers of this time are Balthazar Ayala, a Spanish jurisconsult, who died in 1584, having written in a historico-judicial spirit on the subject of war in his "De Jure et Officiis Belli"; Conrad Brunus, a German jurist, who wrote of the rights and duties of ambassadors in his "De Legationibus," published in 1548; and pre-eminent above all, Albericus Gentilis, an Italian professor of jurisprudence and lecturer at Oxford, a writer of force and originality, who published his "De Legationibus" in 1583 and his "De Jure Belli" in 1589.