[Sidenote:  The boundary zone in political expansion.]

The significance of the border zone of assimilation for political expansion lies in the fact that it prepares the way for the advance of the state boundary from either side; in it the sharp edge of racial and cultural antagonism is removed, or for this antagonism a new affinity may be substituted.  The zone of American settlement, industry, and commerce which in 1836 projected beyond the political boundary of the Sabine River over the eastern part of Mexican Texas facilitated the later incorporation of the State into the Union, just as a few years earlier the Baton Rouge District of Spanish West Florida had gravitated to the United States by reason of the predominant American element there, and thus extended the boundary of Louisiana to the Pearl River.  When the political boundary of Siberia was fixed at the Amur River, the Muscovite government began extending the border zone of assimilation far to the south of that stream by the systematic Russification of Manchuria, with a view to its ultimate annexation.  Schleswig-Holstein and Alsace-Lorraine, by reason of their large German population, have been readily incorporated into the German Empire.  Only in Lorraine has a considerable French element retarded the process.  The considerable sprinkling of Germans over the Baltic provinces of Russia and Poland west of the Vistula, and a certain Teutonic stamp of civilization which these districts have received, would greatly facilitate the eastward extension of the German Empire; while their common religions, both Protestant and Roman Catholic, would help obliterate the old political fissure.  Thus the borderland of a country, so markedly differentiated from its interior, performs a certain historical function, and becomes, as it were, an organ of the living, growing race or state.

[Sidenote:  Tendency toward defection along political frontiers.]

Location on a frontier involves remoteness from the center of national, cultural, and political activities; these reach their greatest intensity in the core of the nation and exercise only an attenuated influence on the far-away borders, unless excellent means of communication keep up a circulation of men, commodities, and ideas between center and periphery.  For the frontier, therefore, the centripetal force is weakened; the centrifugal is strengthened often by the attraction of some neighboring state or tribe, which has established bonds of marriage, trade, and friendly intercourse with the outlying community.  Moreover, the mere infusion of foreign blood, customs, and ideas, especially a foreign religion, which is characteristic of a border zone, invades the national solidarity.  Hence we find that a tendency to political defection constantly manifests itself along the periphery.  A long reach weakens the arm of authority, especially where serious geographical barriers intervene; hence border uprisings are usually successful, at least for a time.  When accomplished, they involve that shrinkage of the frontiers which we have found to be the unmistakable symptom of national decline.