In the century from 1815 to 1914 the law of nations became international law. Several factors contributed to this change.

The Congress of Vienna is a convenient starting point because it both epitomized and symbolized what was to follow. Here in 1815 the great nations assembled to legislate not merely for Europe, but for the world. Thus the Congress marks a formal recognition of the political system that was central to world politics for a century. International law had to fit the conditions of Europe, and nothing that could not fit this system, or the interests of the great European nations collectively, could possibly emerge as law in any meaningful sense. Essentially this imposed two conditions: First, international law had to recognize and be compatible with an international political system in which a number of states were competitive, suspicious, and opportunistic in their political alignments with one another; second, it had to be compatible with the value system that they shared. In both respects, international law was Europeanized.

It was not always easy to develop theory and doctrine which would square the two conditions. On the one hand, the major European nations had to maintain vis-a-vis each other an emphasis upon sovereignty, independence, formal equality -- thus insuring for themselves individually an optimal freedom of action to maintain the ``flexibility of alignment'' that the system required and to avoid anything approaching a repetition of the disastrous Napoleonic experience. But there was no pressing need to maintain these same standards with regard to most of the rest of the world. Thus, theory and doctrine applicable among the great nations and the smaller European states did not really comfortably fit less developed and less powerful societies elsewhere. Political interference in Africa and Asia and even in Latin America (though limited in Latin America by the special interest of the United States as expressed in the Monroe Doctrine, itself from the outset related to European politics and long dependent upon the ``balance of power'' system in Europe) was necessary in order to preserve both common economic values and the European ``balance'' itself. A nation such as Switzerland could be neutralized by agreement and could be relied upon to protect its neutrality; more doubtful, but possible, (with an assist from the North) was the neutralization of the Latin American countries; out of the question was the neutralization of Asia and Africa.