According To Oswald Spengler

Oswald Spengler wrote the spectacular opus The Decline of the West shortly before WWI and the book was published in Germany in 1918, provoking universal reflections on man and civilization. The following passage is found on pages 104-105 in volume 2 of the 1961 Knopf edition:

When the ordinary thought of a highly cultivated people begins to regard "having children" as a question of pro's and con's, the great turning-point has come. For Nature knows nothing of pro and con. Everywhere, wherever life is actual, reigns an inward organic logic, an "it," a drive, that is utterly independent of waking-being, with its causal linkages, and indeed not even observed by it. The abundant proliferation of primitive peoples is a natural phenomenon, which is not even thought about, still less judged as to its utility or the reverse. When reasons have to be put forward at all in a question of life, life itself has become questionable. At that point begins prudent limitation of the number of births. In the Classical world the practice was deplored by Polybius as the ruin of Greece, and yet even at his date it had long been established in great cities; in subsequent Roman times it became appallingly general. At first explained by the economic misery of the times, very soon it ceased to explain itself at all. And at that point, too, in Buddhist India as in Babylon, in Rome as in our own cities, a man's choice of the woman who is to be, not mother of his children as amongst peasants and primitives, but his own "companion for life," becomes a problem of mentalities. The Ibsen marriage appears, the "higher spiritual affinity" in which both parties are "free"--free, that is, as intelligences, free from the plantlike urge of the blood to continue itself, and it becomes possible for a Shaw to say "that unless Woman repudiates her womanliness, her duty to her husband, to her children, to society, to the law, and to everyone but herself, she cannot emancipate herself." The primary woman, the peasant woman, is mother. The whole vocation towards which she has yearned from childhood is included in that one word. But now emerges the Ibsen woman, the comrade, the heroine of a whole megalopolitan literature from Northern drama to Parisian novel. Instead of children, she has soul-conflicts; marriage is a craft-art for the achievement of "mutual understanding". It is all the same whether the case against children is the American lady's who would not miss a season for anything, or the Parisienne's who fears that her lover would leave her, or an Ibsen heroine's who "belongs to herself"--they all belong to themselves and they are all unfruitful. The same fact, in conjunction with the same arguments, is to be found in the Alexandrian, in the Roman, and, as a matter of course, in every other civilized society--and conspicuously in that in which Buddha grew up. And in Hellenism and in the nineteenth century, as in the times of Lao-Tzu and the Charvaka doctrine, there is an ethic for childless intelligences, and a literature about the inner conflicts of Nora and Nana. The "quiverful," which was still an honourable enough spectacle in the days of Werther, becomes something rather provincial. The father of many children is for the great city a subject for caricature; Ibsen did not fail to note it, and presented it in his Love's Comedy.

At this level all Civilizations enter upon a stage, which lasts for centuries, of appalling depopulation. The whole pyramid of cultural man vanishes. It crumbles from the summit, first the world-cities, then the provincial forms, and finally the land itself, whose best blood has incontinently poured into the towns, merely to bolster them up awhile. At the last, only the primitive blood remains, alive, but robbed of its strongest and most promising elements. This residue is the Fellah type.