Much farther down in the cultural scale we find the fisher tribes of Central Africa extending their villages from point to point along the equatorial streams, and the river Indians of South America gradually spreading from headwaters to estuary, and thence to the related environment of the coast. The Tupis, essentially a water race, have left traces of their occupation only where river or coast enabled them to live by their inherited aptitudes.[205] The distribution of the ancient mounds in North America shows their builders to have sought with few exceptions protected sites near alluvial lowlands, commanding rich soil for cultivation and the fish supply from the nearby river. Mountaineer folk often move from one upland district to another, as did the Lombards of Alpine Pannonia in their conquest of Lombardy and Apennine Italy, where all their four duchies were restricted to the highlands of the peninsula.[206] The conquests of the ancient Incas and the spread of their race covered one Andean valley after another for a stretch of one thousand five hundred miles, wherever climatic and physical conditions were favorable to their irrigated tillage and highland herds of llamas. They found it easier to climb pass after pass and mount to ever higher altitudes, rather than descend to the suffocating coasts where neither man nor beast could long survive, though they pushed the political boundary finally to the seaboard. [Map page 101.]
Movement to better geographic conditions.
The search for better land, milder climate, and easier conditions of living starts many a movement of peoples which, in view of their purpose, necessarily leads them into an environment sharply contrasted to their original habitat. Such has been the radial outflow of the Mongoloid tribes down from the rugged highlands of central Asia to the fertile river lowlands of the peripheral lands; the descent of the Iran pastors upon the agricultural folk of the Indus, Ganges and Mesopotamian valleys, and the swoop of desert-born conquerors upon the unresisting tillers of well-watered fields in all times, from the ancient Hyksos of the Nile to the modern Fulbe of the Niger Valley.
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 Völkerwanderungen 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.
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.