International Order

As a series of small kingdoms emerged in Europe out of the ruins of the Carolingian world, a new conception of international order emerged, the notion that there is a natural right order of the world that human understanding could comprehend. This new approach conceived of human society as hierarchical, with lesser societies subordinate to higher ones. Recognition of the natural right order and the acceptance of a society's place within that order was the key to international harmony. To a great extent those who saw the world in these terms differed only on the issue of who would head the hierarchical structure and mediate international conflicts, the Holy Roman Emperor or the pope. Supporters of the imperial position argued that the Christian Roman emperor was the true dominus mundi, the Lord of the World, and the kings of Europe were rulers of what were in effect provinces of the empire. The other view was that the pope as the spiritual head of Christian society was the head of an international society and that he was the ultimate regulator of international order. These competing views about the leadership of Christian society provided one of the fundamental elements of the medieval church-state conflict.

By the thirteenth century, the papal vision of a Christian world order came to dominate, because the emperors could not impose their claim to suzerainty over the kings of Europe. Increasingly kings claimed that within their own kingdoms they possessed the powers attributed to the emperor in the empire, that is they were claiming to be sovereign and therefore not subject to any other temporal ruler. They could not, however, claim exemption from papal jurisdiction. The papal legal system, the canon law, operated throughout the entire Western Christian world, and the pope acted as the judex omnium, the judge of all Christians, even emperors and kings. With regard to international order, the papal approach assumed that all serious issues fell under the jurisdiction of the canon law so that international conflicts, clearly among the most serious of issues, should be brought to the papal court for adjudication. One consequence of the papal conception of the world was that several thirteenth-century popes intervened in conflicts between Christian kings in order to prevent wars and to keep the peace. Another aspect of medieval thought on international order concerned Christian relations with non-Christian societies, especially Muslim societies. The emergence of Islam in seventh-century Arabia led to the creation of the Dar al-Islam ("the abode of Islam"), a Muslim cultural and social order that contended with Christendom militarily and spiritually for the next thousand years along a line that stretched from eastern Europe, through the Near East, and across North Africa and into Spain. Was it possible for Christians to live at peace with such neighbors? In practice, throughout the Middle Ages, Christians and Muslims engaged in trade throughout the Mediterranean, demonstrating that peaceful relations were possible under some conditions. Furthermore, until the eleventh century, Christian pilgrims were generally able to go on pilgrimage to the Holy Land and visit the places associated with the life of Christ, even though Palestine had been in Muslim hands since the fall of Jerusalem in 638.

The call for a crusade to free the Holy Land in 1095 was a crucial turning point in relations between Christians and Muslims, because Christians claimed the right to regain possession of Christian lands previously conquered by the Muslims as well as the right to protect themselves against advancing Muslim armies. The crusade was also seen as a means for developing a peaceful Christian world by diverting the violent to the frontier with the Muslims. At the same time, however, the crusaders also contributed to the deepening split within the Christian world between the Latin Church of Europe and the Greek Church of the Byzantine Empire. They did this by refusing to restore the lands they conquered from the Muslims to Byzantine control and by imposing the Latin ritual and Latin bishops on the Christian peoples of the East, peoples that adhered to versions of Christianity deemed heretical by the papacy.

In the mid-thirteenth century, Pope Innocent IV (r. 1243–1254), a leading canon lawyer, outlined a kind of world legal order under papal direction. He argued that the pope was the ultimate judge of all humankind, judging men and women according to the law to which they were subject. Thus, the pope judged Christians according to the canon law, Jews according to the Law of Moses, and all other people by the terms of the natural law that is accessible to all rational human beings. Such a vision was impossible to realize even within Christian Europe, but the canon lawyers may have been the first thinkers to conceive of all humankind as ultimately forming a community with a universal legal order and therefore the first thinkers to suggest the possibility of a formal set of rules to regulate international relations. Subsequently, a leading ecclesiastical thinker, Nicholas of Cusa (1401–1464), published his De Concordantia Catholica, an outline of the medieval Christian conception of an orderly world, a world in which every kingdom and principality, Christian and non-Christian, functioned within its proper place.

A second medieval approach to the problem of international order appeared in the De Monarchia of the poet Dante Alighieri (1265–1321). Like the ecclesiastical conception of world order, Dante conceived of mankind as a single community but under the jurisdiction of the Holy Roman Emperor who was, according to Roman Law, the dominus mundi, the Lord of the World. Dante's primary interest was in regulating relations among the European states in order to end the constant round of wars.

During the Middle Ages, discussions of world order did not progress beyond the theoretical level. These theories assumed that humankind potentially formed a single human community subject to enforceable universal legal standards and functionally organized in a hierarchically constructed system under papal or imperial leadership. Such theories were based on a limited knowledge of the actual geography of the earth and its inhabitants. Around 1500, two events radically undermined these medieval theories of world order: the voyages of Columbus and the Protestant Reformation. Columbus's voyages revealed to Europeans for the first time the vastness of the sea and the diversity of the earth's population. The Protestant Reformers rejected the papacy and the entire ecclesiastical structure that the popes headed and therefore rejected the hierarchical conception of world order associated with it. These developments reshaped discussions of world order, dividing discussion into several distinct topics. These included: order among the nations of Europe; access to and jurisdiction over the sea; and the rights of the peoples of the New World in the face of European expansion.