The varied struggles of the middle period from the beginning of the Christian Era to the middle of the seventeenth century had a decided influence upon the body and form of international law.

Roman Empire

The growth of the Roman Empire, as the single world power and sole source of political authority, left small need of international standards. The appeal in case of disagreement was not to such standards, but to Cæsar. The idea of one common supremacy was deep-rooted. Political assimilation followed the expansion of political privileges.

The Church

 A similar unifying influence was found in the growth of the Christian Church which knew no distinction bond or free, Jew or Gentile. Christianity, called to be the state religion early in the fourth century, modeled its organization on that of the Roman Empire; and from the sixth century, with the decay of the Empire, the Church became the great power. The belief in the eternity and universality of Roman dominion was strengthened by the Church, although materially changed in its nature. Whatever the inconsistencies in Church and State during the first ten centuries of our era, there had grown up the idea, of great importance for international law, that there could be a ground upon which all might meet, a belief which all might accept, both in regard to political and religious organization. For five hundred years before the days of Boniface VIII. (1294-1303), the holder of the papal office had from time to time acted as an international judge.

The canon law, codified by Gregory IX. (1227-1241), was planned to rival the Corpus Juris Civilis. The Popes, with varying degrees of success, tried to render such international justice as the discordant elements introduced by the growth of cities and rise of nationalities demanded.[24] From the Council of Constance (1414-1418), which was a recognition of the fact of nationality, and at which the emperor for the last time appeared as the great international head, the decline of both the Church and the Empire as direct international factors was rapid.


By the eleventh century feudalism had enmeshed both the temporal and spiritual authorities. This system, closely related to the possession of land and gradation of classes, discouraged the development of the ideas of equality of state powers necessary for the development of international law, though it did emphasize the doctrine of sovereignty as based on land in distinction from the personal sovereignty of earlier days.

The Crusades

(1096-1270), uniting Christendom against the Saracen for foreign intervention, awakening Europe to a new civilization, expanding the study and practice of the Roman law which feudal courts had checked, weakening many feudal overlords, enfranchising towns, freeing the third estate, spreading the use of the Latin language, enlarging and diversifying commerce, teaching the possible unity of national interests, led to the apprehension of a broader basis in comity which made the growth of interstate relations more rapid.


The code of chivalry and the respect for honor which it enjoined introduced a basis of equable dealing which on account of the international character of the orders of chivalry reacted upon state practice throughout Christian Europe.

Commerce and Sea Laws

 The expansion of commerce, especially maritime, emphasized the duties and rights of nations. The old Rhodian laws of commerce, which had in part been incorporated in and expanded by the Roman code during the days before the overthrow of the Empire, formed a basis for maritime intercourse. From the fall of the Empire to the Crusades commerce was attended with great dangers from pirates on the sea and from exactions in the port. The so-called Amalfitan Tables seem to have been the sea law of the latter part of the eleventh century.

The much more detailed Consolato del Mare of doubtful origin between the twelfth and fourteenth centuries derived some of its principles from the eleventh-century code. The Consolato was recognized by maritime powers as generally binding, and made possible wide commercial intercourse. Many of its principles have stood to the present day, though touching such questions as the mutual rights of neutrals and belligerents on the sea in time of war. As the Consolato formed the code of Southern Europe, the Laws of Oleron formed the maritime code for Western Europe, and were compiled the latter part of the twelfth century, whether by Richard I. or by his mother Queen Eleanor is a disputed question. These laws are based in large measure on the other existing systems.

The Laws of Wisby, dating from about 1288, supplemented the Laws of Oleron, and formed the fundamental law of maritime courts of the Baltic nations. The Hanseatic League in 1591 compiled a system of marine law, Jus Hanseaticum Maritimum, based on the codes of Western and Northern Europe. The maritime law of Europe was practically unchanged for nearly a hundred years, when systematized in 1673 under Louis XIV. Similar to the maritime codes are the “Customs of Amsterdam,” the “Laws of Antwerp,” and the “Guidon de la Mar.”


Closely connected with the development of maritime law during the latter part of the middle period was the establishment of the office of consul. The consuls, under the title of consules marinariorum et mercatorum, resident in foreign countries, assisted by advice and information the merchants of their own countries, and endeavored to secure to their countrymen such rights and privileges as possible. These seem to have been sent by Pisa early in the eleventh century, and were for some time mainly sent by the Mediterranean countries to the East.

The discovery of America marked a new epoch in territorial and mercantile expansion, and introduced new problems among those handed down from an age of political chaos.

The middle period, with all its inconsistencies in theory and practice, had nevertheless taught men some lessons. The world-empire of Rome showed a common political sovereignty by which the acts of remote territories might be regulated; the world-religion of the Church of the middle period added the idea of a common bond of humanity. Both of these conceptions imbued men’s minds with the possibility of a unity, but a unity in which all other powers should be subordinate to a single power, and not a unity of several sovereign powers acting on established principles.

The feudal system emphasized the territorial basis of sovereignty. The Crusades gave to the Christian peoples of Europe a knowledge and tolerance of each other which the honor of the code of chivalry made more beneficent, while the growth of the free cities opposed the dominance of classes feudal or religious. The fluctuations and uncertainties in theory and practice of international intercourse, both in peace and war, made men ready to hear the voice of Grotius (1583-1645), whose work marks the beginning of the modern period.