There are those who maintain that the territorial results are unstable and hence relatively unimportant, liable to speedy readjustment in a fluid state of international relations, subordinated in ever increasing degree to economic and social influences which transcend national boundaries. All this the future must determine. For the present the decisive fact for many millions of Europeans is that they are on one side or another of a political frontier, members or not of the state to which their natural allegiance gravitates; and this is a matter of specific boundary. One may deplore the rivalries over small bits of territory, which acquire a factitious significance in the course of the dispute, but they cannot be ignored. The possession of land is still a passion of peoples, and even of what our census calls ‘minor civil divisions,’ and the history of individual ownership shows that such passions do not grow less with the growth of other interests. So long as states continue to exercise authority within definitely recognized frontiers, the establishing of their territorial limits must remain a fundamental problem of international relations. If an illustration of the meaning of frontiers is desired nearer home, one has only to look at the two sides of the Rio Grande. * * * * * Reduced to their lowest terms, the elements which enter into a national boundary are two, the land and the people; and an ideally perfect frontier would be at the same time geographic and ethnographic. Such coincidences are, however, relatively rare, and the problem varies from age to age as different geographical considerations change in relative importance and as the human elements of race, language, and nationality develop, shift, and grow more complex. Thus a glance at the map of Europe shows that certain frontiers apparently have been drawn by nature, while others are clearly the work of man. The Spanish peninsula, Italy, the British Isles, and the Scandinavian lands are set apart from the mass of the Continent by broad boundaries of sea or mountain which have come to form permanent political frontiers. On the other hand no such obvious natural obstacles separate France from Germany, Germany from Russia, Belgium from Holland, Austria from its neighbors, Serbia from Bulgaria. So far as the boundaries have been drawn by geographic forces, the forces are less obvious; if they have been drawn by the course of history, this requires explanation and elucidation. It so happened that the Paris congress had to do, not with the outlying regions where the physical and the political maps generally coincide, but with those lands of central and eastern Europe where the adjustment is most complicated. We shall understand its work more clearly if we pause to analyze briefly this problem of frontiers.