Primitive peoples carry a drag upon their migrations in their restricted geographical outlook; ignorance robs them of definite goals. The evolution of the historical movement is accelerated by every expansion of the geographical horizon. It progresses most rapidly where the knowledge of outlying or remote lands travels fastest, as along rivers and thalassic coasts. Rome's location as toll-gate keeper of the Tiber gave her knowledge of the upstream country and directed her conquest of its valley; and the movement thus started gathered momentum as it advanced. Cæsar's occupation of Gaul meant to his generation simply the command of the roads leading from the Mediterranean to the northern sources of tin and amber, and the establishment of frontier outposts to protect the land boundaries of Italy; this represented a bold policy of inland expansion for that day. The modern historian sees in that step the momentous advance of history beyond the narrow limits of the Mediterranean basin, and its gradual inclusion of all the Atlantic countries of Europe, through whose maritime enterprise the historical horizon was stretched to include America. In the same way, mediæval trade with the Orient, which had familiarized Europe with distant India and Cathay, developed its full historico-geographical importance when it started the maritime discoveries of the fifteenth century. The expansion of the geographical horizon in 1512 to embrace the earth inaugurated a widespread historical movement, which has resulted in the Europeanization of the world.
Civilization and mobility.
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.
Diffusion of culture.
Where a population too great to be dislodged occupies the land, conquest results in the eventual absorption of the victors and their civilization by the native folk, as happened to the Lombards in Italy, the Vandals in Africa and the Normans in England. Where the invaders are markedly superior in culture though numerically weak, conquest results in the gradual permeation of the conquered with the religion, economic methods, language, and customs of the new-comers.[141] The latter process, too, is always attended by some intermixture of blood, where no race repulsion exists, but this is small in comparison to the diffusion of civilization. This was the method by which Greek traders and colonists Hellenized the countries about the eastern Mediterranean, and spread their culture far back from the shores which their settlements had appropriated. In this way Saracen armies soon after the death of Mohammed Arabized the whole eastern and southern sides of the Mediterranean from Syria to Spain, and Arab merchants set the stamp of their language and religion on the coasts of East Africa as far as Moçambique. The handful of Spanish adventurers who came upon the relatively dense populations of Mexico and Peru left among them a civilization essentially European, but only a thin strain of Castilian blood. Thus the immigration of small bands of people sufficed to influence the culture of that big territory known as Latin America.
Ethnic intermixture.
That vast sum of migrations, great and small, which we group under the general term of historical movement has involved an endless mingling of races and cultures. As Professor Petrie has remarked, the prevalent notion that in prehistoric times races were pure and unmixed is without foundation. An examination of the various forms of the historical movement reveals the extent and complexity of this mingling process.