It is necessary to give to this section the title of international relations between ancient nations, for international law during this period was non-existent. The natural state between foreign nations was universally considered to be war. Peace could only exist as the result of express treaties. Nations were enemies or allies; there was, in theory, no middle ground.

The Greeks came the nearest among ancient nations to acquiring a conception of a system of international law; but their work along this line was limited in the scope of its applications to the inter-relations of the various Greek states. To the ancient Greek the inhabitants of the world were divided into Greeks and Barbarians, and however carefully the relations among the former might be regulated, nothing but mutual hostility and contempt was to be expected between the former and the latter.

The foreign policy of the Romans was through its whole period a most aggressive one. At the time of the highest development of the Roman Empire, Rome was surrounded on the north, south, and west by uncivilized or semi-civilized races, while their relation with the New Persian Empire on the east was one of almost unbroken hostility.

The development of any system of international law during a period of this character was an impossibility.