d is still sometimes repeated, that the pressure of
over-population is the chief cause of wars. That is a statement which
requires a very great deal of qualification. It is, indeed, possible
that the great hordes of warlike barbarians from the North and the East
which invaded Europe in early times, sometimes more or less overwhelming
the civilized world, were the result of a rise in the birth-rate and an
excess of population beyond the means of subsistence. But this is far
from certain, for we know absolutely nothing concerning the birth-rate
of these invading peoples either before or during the period of their
incursions. Again, it is certain that, in modern times, a high and
rising birth-rate presents a favourable condition for war. A war
distracts attention from the domestic disturbances and economic
wretchedness which a too rapid growth of population necessarily
produces, while at the same time tending to draw away and destroy the
surplus population which causes this disturbance and wretchedness. Yet
there are other ways of meeting this over-population beside the crude
method of war. Social reform and emigration furnish equally effective
and much more humane methods of counteracting such pressure. No doubt
the over-population resulting from an excessively high birth-rate, when
not met, as it tends to be, by a correspondingly high death-rate from
disease, may be regarded as a predisposing cause of war, but to assert
that it is the pre-eminent cause is to go far beyond the evidence at
present available.

To whatever degree, however, it may have been potent in causing war in
the past, it is certain that the pressure of population as a cause of
war will be eliminated in the future. The only nations nowadays that can
afford to make war on the grand scale are the wealthy and civilized
nations. But civilization excludes a high birth-rate: there has never
been any exception to that law, nor can we conceive any exceptions, for
it is more than a social law; it is a biological law. Russia, a still
imperfectly civilized country, stands apart in having a very high
birth-rate, but it also has a very high death-rate, and even should it
happen that in Russia improved social conditions lower the death-rate
before affecting the birth-rate, there is still ample room within
Russian territory for the consequent increase of population. Among all
the other nations which are considered to threaten the world's peace,
the birth-rate is rapid