As illustrations of the variations that have occurred in the population of different countries, may be mentioned the immense diminution of that of Italy in consequence of the wars of Justinian; the depopulation of North Africa in consequence of theological quarrels; its restoration through the establishment of Mohammedanism; the increase of that of all Europe through the feudal system, when estates became more valuable in proportion to the number of retainers they could supply.  The crusades caused a sensible diminution, not only through the enormous army losses, but also by reason of the withdrawal of so many able-bodied men from marriage-life.  Similar variations have occurred on the American Continent.  The population of Mexico was very quickly diminished by two million through the rapacity and atrocious cruelty of the Spaniards, who drove the civilized Indians to despair.  The same happened in Peru.

The population of England at the Norman conquest was about two million.  In five hundred years it had scarcely doubled.  It may be supposed that this stationary condition was to some extent induced by the papal policy of the enforcement of celibacy in the clergy.  The “legal generative force” was doubtless affected by that policy, the “actual generative force” was not.  For those who have made this subject their study have long ago been satisfied that public celibacy is private wickedness.  This mainly determined the laity, as well as the government in England, to suppress the monasteries.  It was openly asserted that there were one hundred thousand women in England made dissolute by the clergy.

In my history of the “American Civil War,” I have presented some reflections on this point, which I will take the liberty of quoting here:  “What, then, does this stationary condition of the population mean?  It means, food obtained with hardship, insufficient clothing, personal uncleanness, cabins that could not keep out the weather, the destructive effects of cold and heat, miasm, want of sanitary provisions, absence of physicians, uselessness of shrine-cure, the deceptiveness of miracles, in which society was putting its trust; or, to sum up a long catalogue of sorrows, wants, and sufferings, in one term—­it means a high death-rate.

“But more; it means deficient births.  And what does that point out?  Marriage postponed, licentious life, private wickedness, demoralized society.

“To an American, who lives in a country that was yesterday an interminable and impenetrable desert, but which to-day is filling with a population doubling itself every twenty-five years at the prescribed rate, this awful waste of actual and contingent life cannot but be a most surprising fact.  His curiosity will lead him to inquire what kind of system that could have been which was pretending to guide and develop society, but which must be held responsible for this prodigious destruction, excelling, in its insidious result, war, pestilence, and famine combined; insidious, for men were actually believing that it secured their highest temporal interests.  How different now!  In England, the, same geographical surface is sustaining ten times the population of that day, and sending forth its emigrating swarms.  Let him, who looks back, with veneration on the past, settle in his own mind what such a system could have been worth.”