The expansion of the Japanese into Korea and Saghalin is undoubtedly such a return current, after an interval long enough to work a complete transformation in the primitive Mongolians who found their way to that island home.  Sometimes the return represents the ebbing of the tide, rather than the back water of a stream in flood.  Such was the retreat of the Moors from Spain to the Berber districts of North Africa, whither they carried echoes of the brilliant Saracen civilization in the Iberian Peninsula.  Such has been the gradual withdrawal of the Turks from Europe back to their native Asia, and slow expulsion of the Tartar tribes from Russia to the barren Asiatic limits of their former territory. [See map page 225.]

[Sidenote:  Regions of attraction and repulsion.]

Voluntary historical movements, seeking congenial or choice regions of the earth, have left its less favored spots undisturbed.  Paucity of resources and isolation have generally insured to a region a peaceful history; natural wealth has always brought the conqueror.  In ancient Greece the fruitful plains of Thessaly, Boeotia, Elis and Laconia had a fatal attraction for every migrating horde; Attica’s rugged surface, poor soil, and side-tracked location off the main line of travel between Hellas and the Peloponnesus saved it from many a rough visitant,[210] and hence left the Athenians, according to Thucydides, an indigenous race.  The fertility of the Rhine Valley has always attracted invasion, the barren Black Forest range has repelled and obstructed it.

The security of such unproductive highlands lies more in their failure to attract than in their power to resist conquest.  When to abundant natural resources, a single spot adds a reputation for wealth, magnificence, an exceptional position for the control of territory or commerce, it becomes a geographical magnet.  Such was Delphi for the Gauls of the Balkan Peninsula in the third century, Rome for the Germanic and Hunnish tribes of the Voelkerwanderung, Constantinople for the Normans, Turks and Russians, Venice for land-locked Austria, the Mississippi highway and the outlet at New Orleans for our Trans-Allegheny pioneers.

[Sidenote:  Psychical influences in certain movements.]

Sometimes the goal is fabulous or mythical, but potent to lure, like the land of El Dorado, abounding in gold and jewels, which for two centuries spurred on Spanish exploration in America.  Other than purely material motives may initiate or maintain such a movement, an ideal or a dream of good, like the fountain of eternal youth which brought Ponce de Leon to Florida, the search for the Islands of the Blessed, or the spirit of religious propaganda which stimulated the spread of the Spanish in Mexico and the French in Canada, or the hope of religious toleration which has drawn Quaker, Puritan, Huguenot, and Jew to America.  It was an idea of purely spiritual import which directed the century-long movement of the Crusades toward Jerusalem,