[Sidenote:  Southward and westward drifts in the northern hemisphere.]

The attraction of a milder climate has caused in the northern hemisphere a constantly recurring migration from north to south.  In primitive North America, along the whole broad Atlantic slope, the predominant direction of Indian migrations was from north to south, accompanied by a drift from west to east.[207] On the Pacific side of the continent also the trend was southward.  This is generally conceded regardless of theory as to whether the Indians first found entrance to the continent at its northeast or northwest corner.  It was a movement toward milder climates.[208] Study of the Voelkerwanderungen in Europe reveals two currents or drifts in varied combination, one from north to south and the other from east to west, but both of them aimed at regions of better climate; for the milder temperature and more abundant rainfall of western Europe made a country as alluring to the Goths, Huns, Alans, Slavs, Bulgars and Tartars of Asiatic deserts and Russian steppes, as were the sunny Mediterranean peninsulas to the dwellers of the bleak Baltic coasts.  This is one geographic fact back of the conspicuous westward movement formulated into an historical principle:  “Westward the star of empire takes its course.”  The establishment of European colonies on the western side of the Atlantic, their extension thence to the Pacific and ever westward, till European culture was transplanted to the Philippines by Spain and more recently by the United States, constitute the most remarkable sustained movement made by any one race.

[Sidenote:  Eastward movements.]

But westward movements are not the only ones.  On the Pacific slope of Asia the star has moved eastward.  From highland Mongolia issued the throng which originally populated the lowlands of China; and ever since, one nomad conqueror after the other has descended thence to rule the fruitful plains of Chili and the teeming populations of the Yangtze Valley.[209] Russia, blocked in its hoped for expansion to the west by the strong powers of central Europe, stretched its dominion eastward to the Pacific and for a short time over to Alaska.  The chief expansion of the German people and the German Empire in historical times has also been from west to east; but this eastward advance is probably only retracing the steps taken by many primitive Teutonic tribes as they drifted Rhineward from an earlier habitat along the Vistula.

[Sidenote:  Return movements.]

Since the world is small, it frequently happens that a people after an interval of generations, armed with a higher civilization, will reenter a region which it once left when too crude and untutored to develop the possibilities of the land, but which its better equipment later enables it to exploit.  Thus we find a backward expansion of the Chinese westward to the foot of the Pamir, and an internal colonization of the empire to the Ili feeder of Lake Balkash.