Frontier of a country over regions which the protecting Power is, for whatever reason, unable or unwilling to seize and hold itself, and, while falling short of the full rights of property or sovereignty, it carries with it a considerable degree of control over the policy and international relations of the protected State. It involves the obligation to defend the latter from external attack, and to secure the proper treatment of foreign subjects and property inside it. To what extent it justifies interference in the internal administration of the State is a question admitting of no law.
The Roman Empire is the classical illustration of this policy, though in a somewhat inchoate form, in the ancient world. In the Western Empire Protectorates, strictly so called, were not required because the enemy with whom contact was to be avoided was the barbarian, formidable not from his organization, but from his numbers; and against this danger purely military barriers, whether in Britain, Gaul, Germany, or Africa, required to be employed. But in the East, where the ambitions of Rome for the first time encountered a rival and civilized Power of almost equal strength with itself, namely, the Parthian or Persian Kingdom, the perils of actual contact were for long delayed by a barrier of protected States, the majority under the political suzerainty of Rome, some of them oscillating from one allegiance to another, according to the degree of pressure applied; the most important of all, by reason of its physical features and geographical position, namely, Armenia, having a career which in its stormy vicissitudes has recalled to many writers the chequered and fateful experience, between the rival Powers of Great Britain and Russia,