INTRODUCTION TO SOCIOLOGY 65
make a social frontier. This military frontier has in reality to face in two directions. It must oppose two hostile forces: the exterior enemy, and the more positive and penetrating social forces of which it is the envelope, on one side; and, on the other, its own interior forces, which are incessantly developing them- selves, and which oblige the military frontier to press forward in order to make place for stable, regular, and peaceful communica- tion with the regions over which military protectorate is exercised. Thus progressive civilizations continually chase war before them, expelling it from their own borders and relegating it to remote frontiers. This is a constant law, applicable to petty states as well as to the largest empires.
All frontiers are social, even the military frontiers; and this is why they change continually. It is also why the military form is incapable, as historical experience has proved it to be, of establishing a regular mode of inter-social equilibrium, and why other forms must be substituted. It is a task for the sociologist to discover what is the most advantageous form in a civilization which, like ours, has long since passed the frontiers of the Roman power at the height of its grandeur; in which, nevertheless, narrow military frontiers not at all consistent with the real development of civilization continue to divide people who for a long time have shared a common life.
In his political testament Augustus advised contentment with the limits which he assigned to the empire. He was thus imbued with the idea that there are natural and fixed limits. On the con- trary, every social frontier is variable as the society itself. Indeed, it merely expresses in reality the limits of the power of the society to penetrate surrounding territory limits them- selves variable and diverse, as we have seen, according to the nature of the energies or social capacities and external resistances. The advice of Augustus was wise in appearance, but impracti- cable. To defend itself, a society must be able to attack. Accord- ingly, from Augustus to Trajan, besides temporary acquisitions, the empire annexed Armenia as far as the Caucasus, as well as the eastern shore of the Euxine as far as the Cimmerian Bos- phorus. It also absorbed Cappadocia, Lycia, and the whole
