to their soil are easily ruptured and the people themselves dislodged, while their land is appropriated by the intruder.  But who could ever conceive of dislodging the Chinese or the close-packed millions of India?  A modern state with a given population on a wide area is more vulnerable than another of like population more closely distributed; but the former has the advantage of a reserve territory for future growth.[107] This was the case of Kursachsen and Brandenburg in the sixteenth century, and of the United States throughout its history.  But beside the danger of inherent weakness before attack, a condition of relative underpopulation always threatens a retardation of development.  Easy-going man needs the prod of a pressing population. [Compare maps pages 8 and 103 for examples.]

[Sidenote:  Land and food supply.]

Food is the urgent and recurrent need of individuals and of society.  It dictates their activities in relation to their land at every stage of economic development, fixes the locality of the encampment or village, and determines the size of the territory from which sustenance is drawn.  The length of residence in one place depends upon whether the springs of its food supply are perennial or intermittent, while the abundance of their flow determines how large a population a given piece of land can support.

[Sidenote:  Advance from natural to artificial basis of subsistence.]

Hunter and fisher folk, relying almost exclusively upon what their land produces of itself, need a large area and derive from it only an irregular food supply, which in winter diminishes to the verge of famine.  The transition to the pastoral stage has meant the substitution of an artificial for a natural basis of subsistence, and therewith a change which more than any other one thing has inaugurated the advance from savagery to civilization.[108] From the standpoint of economics, the forward stride has consisted in the application of capital in the form of flocks and herds to the task of feeding the wandering horde;[109] from the standpoint of alimentation, in the guarantee of a more reliable and generally more nutritious food supply, which enables population to grow more steadily and rapidly; from the standpoint of geography, in the marked reduction in the per capita amount of land necessary to yield an adequate and stable food supply.  Pastoral nomadism can support in a given district of average quality from ten to twenty times as many souls as can the chase; but in this respect is surpassed from twenty to thirty-fold by the more productive agriculture.  While the subsistence of a nomad requires 100 to 200 acres of land, for that of a skillful farmer from 1 to 2 acres suffice.[110] In contrast, the land of the Indians living in the Hudson Bay Territory in 1857 averaged 10 square miles per capita; that of the Indians in the United States in 1825, subsidized moreover by the government, 1-1/4 square miles.[111]