Civilized man is at once more and less mobile than his primitive brother. Every advance in civilization multiplies and tightens the bonds uniting him with his soil; makes him a sedentary instead of a migratory being. On the other hand every advance in civilization is attended by the rapid clearing of the forests, by the construction of bridges and interlacing roads, the invention of more effective vehicles for transportation whereby intercourse increases, and the improvement of navigation to the same end. Civilized man progressively modifies the land which he occupies, removes or reduces obstacles to intercourse, and thereby approximates it to the open plain. Thus far he facilitates movements. But while doing this he also places upon the land a dense population, closely attached to the soil, strong to resist incursion, and for economic reasons inhospitable to any marked accession of population from without. Herein lies the great difference between migration in empty or sparsely inhabited regions, such as predominated when the world was young, and in the densely populated countries of our era. As the earth grew old and humanity multiplied, peoples themselves became the greatest barriers to any massive migrations, till in certain countries of Europe and Asia the historical movement has been reduced to a continual pressure, resulting in compression of population here, repression there. Hence, though political boundaries may shift, ethnic boundaries scarcely budge. The greatest wars of modern Europe have hardly left a trace upon the distribution of its peoples. Only in the Balkan Peninsula, as the frontiers of the Turkish Empire have been forced back from the Danube, the alien Turks have withdrawn to the shrinking territory of the Sultan and especially to Asia Minor. [Sidenote: Diffusion of culture.]