(3) _The Decreasing Pressure of Population._ It was at one time commonly said, and 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.