l 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.

[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