“And law was brought into the world for nothing else, but to limit the natural liberty of particular men, in such manner, as they might not hurt, but assist one another, and join together against a common enemy.” Hobbes's words (1960, 175) remind us forcibly that a body politic or a “state,” whatever else it may be, is a unity organized to protect its members against a real or a potential external enemy. Whatever form a body politic may take, whether it be a tribe or clan, a “city state,” a composite feudal system, a “church state,” or a modern sovereign state, the capacity to engage in an armed contest with adversaries, reflected in a fundamental inner division of labor between military and other occupations, remains a constant characteristic.

Before this is labeled as an uncompromisingly “realist” viewpoint, however, it must be added that another characteristic is equally constant, namely the endeavor of states to introduce some kind of order or regularity into their external relations, to prevent them from being merely a succession of violent encounters. History reveals a primordial effort by political units to establish formal boundary lines between a state of war, or of hostility towards other units, and a state of peace or friendship.