§ 16. #Problem of maximum military power.# It is a grave question, however, whether a nation with a comparatively sparse population, high wages, and great wealth can safely limit that population in the presence of a capable, ambitious, and efficient rival that covets such opportunities. On the one hand, a population may be so sparse that it has not soldiers enough to defend its territory against a numerous enemy; on the other hand, it may be so dense, and consequently average incomes be so low, that it cannot properly train, arm, and support its population of military age. The recent developments in the art of warfare call for great use of the mechanical industries, for great power to endure taxation, and for great financial resources, conditions found only where the average of national income is high. The point of maximum military power must be far short of the maximum possible population. It would seem that a nation of 100,000,000 inhabitants favorably situated to resist aggression, well supplied with the natural materials for munitions, and well equipped to produce them, might safely limit its numbers so as to ensure a high level of popular income. This safety would be greatly increased by permanent alliance with other peoples likewise limiting their numbers and, therefore, interested in maintaining the peace of the world. In this way it would be possible for them all to maintain a standard of popular well-being even higher than is fully consistent with the maximum military power, even in the presence of prolific and aggressive rival nations. [Footnote 1: Even more important than these is the relative decrease of the successful strains of the population, briefly treated in Vol. I, ch. 33. This is the problem of eugenics, the choice and biologic breeding of capable men to be the citizens of the nation, and broadly understood, it includes both the negro and the immigrant problems.] [Footnote 2: See Vol. I, p. 430, figure 58, showing the fall in the decennial rate of increase of negroes compared with whites; and see comment in accompanying note.] [Footnote 3: See above, ch. 20, sec. 11, and references in note.] [Footnote 4: See below, sec. 12.] [Footnote 5: See Vol. I, p. 221, on non-competing classes.] [Footnote 6: The latest and best statement is that of H.P. Fairchild, "Immigration," pp. 215-225, citing various opinions, and accepting the view of Walker. But he says (p. 216): "It must be admitted that this is not a proposition which can be demonstrated in an absolutely mathematical way, which will leave no further ground for argument."] [Footnote 7: See Vol. I, p. 429, for figures of population and of decennial rates of increase.] [Footnote 8: The effect of the growth of cities is discussed in the "American Journal of Sociology," Vol. 18, p. 342, in an article on "Walker's Theory of Immigration," by E.A. Goldenweiser.] [Footnote 9: See Vol. I, p. 420.] [Footnote 10: See Vol. I, chs. 34 and 35.]