hold.  A period of drought, or pressure by rivals, in former times sent a horde of these hardy shepherds on a raid into the nearest settled province; and if, like the Tartars, they were mounted, they usually killed, plundered, and conquered wherever they went, until the discovery of gunpowder saved civilisation from the recurrent peril of barbarian inroads.  Barbarians of another type, hunters with fixed homes, seldom increase rapidly, partly because the dangers of forest-life for young children are much greater than on the steppe.

In the primitive river-valley civilisations, such as Egypt and Babylonia, the conditions of increase were so favourable that a dense population soon began to press upon the means of subsistence.  In Egypt the remedy was a centralised government which could undertake great irrigation works and intensive cultivation.  In Babylonia, for the first time in history, foreign trade was made to support a larger population than the land itself could maintain.  There was little or no infanticide in Babylonia, but the death-rate in these steaming alluvial plains has always been very high.

When we turn to poor and mountainous countries like Greece, the conditions are very different.  It was an old belief among the Hellenes that in the days before the Trojan War ’the world was too full of people.’  The increase was doubtless made possible by the trade which developed in the Minoan period, but the sources of food-supply were liable to be interfered with.  Hence came the necessity for active colonisation, which lasted from the eighth to the sixth century B.C.  This period of expansion came to an end when all the available sites were occupied.  In the sixth century the Greeks found themselves headed off, in the west by Phoenicians and Etruscans, in the east by the Persian Empire.  The problem of over-population was again pressing upon them.  Incessant civil wars between Hellenes kept the numbers down to some extent; but Greek battles were not as a rule very bloody, and every healthy nation has a surprising capacity of making good the losses caused by war.  The first effect of the check to emigration was that the old ideal of the ‘self-sufficient life,’ which meant the practice of mixed farming, had to be partially abandoned.  The most flourishing States, and especially Athens, had to take to manufactures, which they exchanged for the food-products of the Balkan States and South Russia.  The result was an increasing urbanisation, and a new population of free ‘resident aliens.’  Conservatives hated this change and wished to revive the old ideal of a small self-supporting State, with a maximum of 20,000 or 30,000 citizens.  Plato, in his latest work, the ‘Laws,’ wishes his model city to be not too near the sea, the proximity of which ’fills the streets with merchants and shopkeepers, and begets dishonesty in the souls of men.’  On the other side Isocrates, the most far-seeing of Athenian politicians, realised that the day of small