This retrospect also leads to the conclusion that the influence of physical features in the formation of European nationalities has been exerted with maximum intensity in the early periods of their history. This was at the time when man’s adaptation to environment was largely blind and unconditioned by his own will. Freedom from this physical thralldom is attained only through man’s practical knowledge of human necessities and a sound vision of the welfare of his descendants. Manifestations of nature can then be made subservient to the human will. In this regard historians may eventually be induced to divide their favorite study into two main periods characterized respectively by man’s submission to, or his intelligent control of, environment. A proper understanding of this conception may contribute to the establishment of frontiers with a view to eliminating conflicts due to relics of national or historical incompatibility. The development of modern boundaries should be regarded as a process originating in barriers first provided by nature and subsequently elaborated by the human will for its purposes. Gradually however natural features of the land lose value as national boundaries. This is the result of man’s progress, of the development of railways or wireless stations. It is the removal of natural obstacles; the conquest of distance by speed. All these advances tend to promote intercourse. They are opening the vista of a day when an international boundary will have no greater importance in world affairs than the limiting line of a city plot. National frontiers, at best, become established by virtue of historical accidents. At given times and in order to promote fellowship among nations it becomes necessary to define the areas over which certain principles of political jurisdiction are recognized as valid by a given body of men. A national frontier in the strictest sense of the term cannot, therefore, be limited by the surface feature which has shaped its development. It has generally outgrown this phase of its extension together with the constantly increasing range of activity of the peoples it once inclosed. Factors of an ethnological, economic or linguistic nature must, therefore, be considered. Then only will the new delimitation be entitled to be qualified as natural.