n upon a fixed
area produces an increased density, unless certain social forces
counteract it. Without these forces, the relation of men to the land
would have tended to modify everywhere in the same way. Increase in
numbers would have been attended by a corresponding decrease in the
amount of land at the disposal of each individual. Those states which,
like Norway and Switzerland, cannot expand and which have exploited
their natural resources to the utmost, must resign themselves to the
emigration of their redundant population. But those which have remained
within their own boundaries and have adopted a policy of isolation, like
China, feudal Japan during its two and a half centuries of seclusion,
and numerous Polynesian islands, have been forced to war with nature
itself by checking the operation of the law of natural increase. All the
repulsive devices contributing to this end, whether infanticide,
abortion, cannibalism, the sanctioned murder of the aged and infirm,
honorable suicide, polyandry or persistent war, are the social
deformities consequent upon suppressed growth. Such artificial checks
upon population are more conspicuous in natural regions with sharply
defined boundaries, like islands and oases, as Malthus observed;[123] but
they are visible also among savage tribes whose boundaries are fixed not
by natural features but by the mutual repulsion and rivalry
characterizing the stage of development, and whose limit of population
is reduced by their low economic status.

[Sidenote: Extra-territorial relations.]

There is a great difference between those states whose inhabitants
subsist exclusively from the products of their own country and those
which rely more or less upon other lands. Great industrial states, like
England and Germany, which derive only a portion of their food and raw
material from their own territory, supply their dense populations
through international trade. Interruption of such foreign commerce is
disastrous to the population at home; hence the state by a navy protects
the lines of communication with those far-away lands of wheat fields and
cattle ranch. This is no purely modern development. Athens in the time
of Pericles used her navy not only to secure her political domination in
the Aegean, but also her connections with the colonial wheat lands
about the Euxine.

The modern state strives to render this circle of trade both large and
permanent by means of commercial treaties, customs