gh, serve to-day as watch-towers for herdsmen tending their
flocks.[1048] Similarly the Bou-bous, inhabiting the flat grasslands of
the French Congo between the Shari and Ubangui Rivers, use the low
knolls dotted over their country, probably old ant-hills, as lookout
points against raiders.[1049] The sand hills and ridges which border the
southern edges of the North German lowland form districts sharply
contrasted to the swampy, wooded depressions of the old deserted river
valleys just to the north. Early occupied by a German stock, they
furnished the first German colonists to displace the primitive Slav
population surviving in those unattractive, inaccessible regions, as
seen in the Spreewald near Kottbus to-day.

[Sidenote: Plains and political expansion.]

The boundless horizon which is unfavorable to a nascent people endows
them in their belated maturity with the power of mastering large areas.
Political expansion is the dominant characteristic of the peoples of the
plains. Haxthausen observed that handicapped and retarded Russia
commands every geographic condition and national trait necessary for
virile and expansive political power.[1050] Muscovite expansion eastward
across the lowlands of Europe and Asia is paralleled by the rapid
spread of American settlement and dominion across the plains and
prairies of the Mississippi Valley, and Hungarian domination of the wide
Danubian levels from the foot-hills of the Austrian Alps to the far
Carpathian watershed. It was the closely linked lowlands of the Seine
and Loire which formed the core of political expansion and
centralization in France. Nearly the whole northern lowland of Germany
has been gradually absorbed by the kingdom of Prussia, which now
comprises in its territory almost two-thirds of the total area of the
Empire. Prussian statesmen formulated the policy of German unification
and colonial expansion, and to Prussia fell the hereditary headship of
the Empire.

Lowland states tend to stretch out and out to boundaries which depend
more upon the reach of the central authority than upon physical
features. We have seen American settlement and dominion overleap one
natural boundary after another between the Mississippi River and the
Pacific, from 1804 to 1848. Russia in an equally short period has pushed
forward its Asiatic frontier at a dozen points, despite all barriers of
desert and mountain. Argentina, blessed with extensive plains, fertile
soil and temperate