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.