ettled till
the Middle Ages. In the United States, the flood of population had
spread westward by 1840 to the ninety-fifth meridian and the north-south
course of the Missouri River; but out of this sea of settlement the
Adirondack Mountains, a few scattered spots in the Appalachians, and the
Ozark Highlands rose as so many islands of uninhabited wilderness, and
they remain to-day areas of sparser population. In 1800, the "bare
spots" in the eastern mountains were more pronounced. [See map page
156.] Great stretches of the Rocky Mountains, of the Laurentian
Highlands of Canada, like smaller patches in the Scandinavian and Swiss
Alps, are practically uninhabited.

[Sidenote: Mountains as transit regions.]

Mountain regions, like deserts and seas, become mere transit districts,
which man traverses as quickly as possible. Hence they often lie as
great inert areas in the midst of active historical lands, and first
appear upon the historical stage in minor roles, when they are wanted by
the plains people as a passway to desirable regions beyond. Then, as a
rule, only their transit routes are secured, while the less accessible
regions are ignored. Caesar makes no mention of the Alps, except to state
that he has crossed them, until some of the mountain tribes try to block
the passage of Roman merchants or armies; then they become important
enough to be conquered. It was not till after the Cimbri in 102 B.C.
invaded Italy by the Brenner route, that the Romans realized the value
of Rhaetia (Tyrol) as a thoroughfare from Italy to Germany, and began
its conquest in 36 B.C. This was the same value which the Tyrol so long
had for the old German Empire and later for Austria,--merely to secure
connection with the Po Valley. The need of land communication with the
Rhone Valley led the Romans to attack the Salyes, who inhabited the
Maritime Alps, and after eighty years of war to force from them the
concession of a narrow transit strip, twelve stadia or one and a half
miles wide, for the purpose of making a road to Massilia.[1188] The
necessity of controlling such transit lands has drawn British India into
the occupation of mountain Baluchistan, Kashmir and Sikkim, just as it
has caused the highlands of Afghanistan to figure actively in the
expansion policy of both India and Russia. The conquest of such transit
lands has always been attended by road building, from the construction
of the Roman highway through the Brenner Pass to the mode