The foundations of Public International Law as it is understood today lie firmly in the development of political relations between the Western European States some 400 years ago. However, certain basic concepts of this Law can be traced back thousands of years ago, in relations between ancient political entities, such as of the Near East, Greece and Persia.
The structure and development of Public International Law is connected with the era of sovereign national States dealing with each other as independent entities. In this sense, therefore, the history of this Law can be regarded as beginning in the 16thCentury with the emergence of independent nation-states from the ruins of the medieval Holy Roman Empire which was based on the claims to universal authority of the Pope as the spiritual, and the Emperor as the temporal, head of Christian nations of Europe. As this Empire disintegrated, a growing number of independent and equal States filled the gap.
The Emergence of independent and equal States subject to no temporal superior authority led to new political theories. The most prominent among these theories was the theory of Sovereignty. This theory was explicitly formulated by Jean Bodin (1530-1596) in his treatise entitled Six Livres de Republique (Six Books on the Republic) of 1576. According to Bodin, in every State there exists in an individual monarch a power called sovereignty (majestas). Sovereignty is a Republic absolute and perpetual power. It is absolute because it is indivisible; however, it is not without any limits. While such a sovereign is not bound by the laws himself instituted, he remains bound by the divine law, the law of nature, and the law of nations. Sovereignty is perpetual because it does not disappear with its holder (the sovereign). The concept of sovereign as supreme legislator, as formulated by Bodin, was in the course of time evolved into the principle which gave the State supreme power vis-à-vis other States.
The coexistence of independent sovereign States led to the development of the system of interstate relations. The need for rules regulating the intercourse between the newly emerging States in Europe stimulated these States to draw mainly upon the Roman Law and the Cannon Law (the Law of Roman-Catholic Church) for the sources of such rules. The significance of the Roman Law and the Cannon Law contribution to “the law of nations” lies not only in the development of a modern system of interstate legal relations, but also in the development of many principles of general equity and “natural law” some of which are similar to certain general principles of law recognized by civilized nations.
In the few centuries that preceded the Thirty Years War (1618-1648), the intensification of international trade, and the improvements in navigation and military techniques, and the discovery of many distant lands by the European States stimulated further development of international practices and the emergence of new conceptions of the law of nations. The intensification of trade led to the conclusion of many commercial treaties and the emergence of new practices and principles related to the law of merchant and the maritime law. Notably, the growth of international trade had from the 8th Century onwards led to the development of international law of merchant and, in particular, to various compilations of maritime law which gained increasing international recognition. The international customs and principles related to the law of merchant and maritime constituted part of the practices and principles of “the law of nations.”
The discovery and subjugation of distant lands and peoples by European States produced numerous conflicting claims of sovereignty, jurisdiction, rights of trade and rights of navigation as well as problems of relations. All these developments urged the Europeans to resort to the Roman Law for helpful norms or analogies, and consequently led to new practices and principles.
By the 17th Century, the growing complexity of international principles, customs and treaties had given rise to their compilation and to the development of further rules governing the conduct of States in time of war and peace. The most important treatise, dealing with States’ relations in time of war and peace, of this period was “De Jure Belli Ac Pacis” (On the Law of War and Peace), published in 1625 by the Dutch jurist and diplomat Hugo Grotius (1583-1645). Hugo Grotius is recognized as the “Father of International Law”, and his treatise is generally regarded as providing the foundation of the Public International Law.
Beside Grotius, there are many jurists who contributed extensively to “the law of nations” during the 17th and the 18thcenturies. Among these jurists are Francisco de Vitoria (1480-1546), Suarez (1548-1617), Alberico Gentili (1552-1608), Samuel von Pufendorf (1632-1694), Richard Zouche (1590-1660), Johann Jakob Moser (1701-1785), Christian Wolff (1676-1754), and Emerich de Vattel (1714-1769).
The International Law (the law of nations) further expanded in the 19th Century. This expansion was due to major events such as the expansion of the European empires, the rise of powerful States both within and outside Europe, the spread of the thought of democracy and nationalism, the Industrial Revolution, the modernization of world transport, and the influence of new inventions.All these events urged the international community to develop the International Law in order to accommodate such events. Consequently, International Law as a law regulating diplomatic and commercial relations between States, and the conduct of war, multiplied and intensified during the 19th Century.
The establishment of the League of Nations in 1919, following the First World War, and the establishment of the United Nations in 1945, following the Second World War, represented two significant turning points in the development of the International Law. The development was characterized by a new departure in the evolution of this Law. International Law began its evolution from being primarily a system of regulating relations between States towards becoming also a system of international cooperation.
The League of Nations was the first international organization established primarily for the purpose of maintaining international peace and security. The establishment of the International Labor Organization (ILO), affiliated with the League of Nations, in 1919 signaled the end of an era in which International Law was, with few exceptions, confined to the regulation of relations between States. The ILO was the first permanent international organization concerned with the improvement of labor conditions and social welfare at the international level. In 1921, the Permanent Court of International Justice (PCIJ) was established as the first permanent international judicial organ with an international judicial jurisdiction.
The establishment of the United Nations in 1945 led to a progressive development of International Law. During the post-United Nations’ era, the development of International Law has been influenced by two major events effected the international community. The first major event has been the expansion in the membership of the international community. New States, mostly representing non-western civilization, have joined the club of family of nations, which was previously exclusively limited to States belonging to Western Civilization. The concerns and priorities of these States have been different from those of other States; they have been occupied with the development of their political, economic and social systems. The second major event has been the massive expansion of international organizations for cooperation. Numerous specialized agencies of the United Nations and other international organizations, universal as well as regional, have been established. This event has confirmed the evolution International Law from its traditional nature to its contemporary nature of being a system of organized collective efforts for cooperation.
Since the establishment of the United Nations, a great number of international treaties covering all aspects of international affaires have been concluded. Law-making treaties have been contributing extensively to the rapid development of Public International Law. They have led to may important new developments in Public International Law, and greatly increased both its scope. Apart of the law-making treaties, international courts, the present International Court of Justice (ICJ), its forerunner the Permanent Court of International Justice (PCIJ), and others, have been also contributing to the development of Public International Law. Moreover, the International Law Commission created in 1947, the organs of the United Nations and its specialized agencies have been playing a significant role in developing and expanding Public International Law.
In conclusion, Public International Law has evolved from being primarily a law of coexistence, which characterized it from its birth in the early 16th century to the mid 20th century, to a law of international organization and cooperation. Moreover, the most important characteristic of Contemporary Public International Law is the steady expansion of its scope through the inclusion of new subject matters formerly outside its sphere, and the inclusion of new participants and subjects such as international organizations and individuals.