[Sidenote:  Contrast of the northern and southern continents.]

From this general law of race movements it follows that certain groups of land-masses, favored by location and large area, play a great imperial role, holding other lands as appanages.  The Eastern Hemisphere, as we have seen, enjoys this advantage over the Western.  Still more the Northern Hemisphere, blessed with an abundance of land and a predominant Temperate Zone location, is able to lord it over the Southern, so insular in its poverty of land.  The history of the Northern Hemisphere is marked by far-reaching historical influences and wide control; that of the Southern, by detachment, aloofness and impotence, due to the small area and isolation of its land-masses.  A subordinate role is its fate.  Australia will always follow in the train of Eurasia, whence alone it has derived its incentives and means of progress.  Neither the southern half of Africa nor South America has ever in historical times struck out a road to advancement unaided by its northern neighbors.  Primitive South America developed the only independent civilization that ever blossomed in the Southern Hemisphere, but the Peruvian achievements in progress were inferior to those of Mexico and Central America.[771]

[Sidenote:  Isolation of the southern continents.]

This subordination of the southern continents is partly due to the fact that they have only one side of contact or neighborhood with any other land, that is, on the north; yet even here the contact is not close.  In Australia the medium of communication is a long bridge of islands; in America, a winding island chain and a mountainous isthmus; in Africa, a broad zone of desert dividing the Mediterranean or Eurasian from the tropical and Negroid part of the continent.  Intercourse was not easy, and produced clear effects only in the case of Africa.  Enlightenment filtering in here was sadly dimmed as it spread.  Moreover it was delayed till the introduction from Asia of the horse and camel, which were not native to Africa, and which, as Ratzel points out, alone made possible the long journey across the Sahara.  The opposite or peninsular sides, running out as great spurs from the compacter land-masses of the north, look southward into vacant wastes of water, find no neighbors in those Antarctic seas.  Owing to this unfavorable location on the edge of things, they were historically dead until four centuries ago, when oceanic navigation opened up the great sea route of the Southern Hemisphere, and for the first time included them in the world’s circle of communication.  But even when lifted by the ensuing Europeanizing process, they only emphasize the fundamental dependence of the Southern Hemisphere upon the superior geographical endowments of the Northern.

[Sidenote:  Effect of continental structure upon historical development.]