For this purpose slavery was calculated: it had two excellent effects with respect to population. The first, that, in unpolished nations, living upon the spontaneous fruits of the earth, and almost continually in war, lives were preserved for the sake of making slaves of the captives. These sold to private people, or different states, were sure of being fed; whereas remaining in their own country, they only occupied a place, which, by the force of the generative faculty, as has been observed, was soon to be filled up by propagation: for it must not be forgot, that when numbers are swept off, by any sudden calamity, which does not proportionally diminish subsistence, a new multiplication immediately takes place. Thus we perceive the hurt done by plagues, by war, and by other devastations, either among men, or cattle, repaired in a few years, even in those countries where the standard number of both is seldom found to increase. What immense quantities of cattle are yearly slaughtered! Does any body imagine that if all were allowed to live, numbers would increase in proportion? The same is true of men. The second advantage of slavery was, that in countries where a good police prevailed, and where the people had fewer wants by far than are felt in modern times, the slaves were forced to labour the soil which fed both them and the idle freemen, as was the case in Sparta; or they filled all the servile places which freemen fill now, and they were likewise employed, as in Greece and in Rome, in supplying with manufactures those whose service was necessary for the state. Here then was a violent method of making mankind laborious in raising food; and providing this be accomplished, (by any means whatever) numbers will increase. Trade, industry, and manufactures, only tend to multiply the numbers of men, by encouraging agriculture. If it be therefore supposed, that two states are equally extended, equally fruitful, and equally cultivated, and the produce consumed at home, I believe they will be found equally peopled. But suppose the one laboured by free men, the other by slaves, what difference will be found in making war? In the first, the free hands must, by their industry and labour, purchase their food, and a day lost in labour is in a manner a day of fasting: in the last, the slaves produce the food, they are first fed, and the rest costs nothing to the body of free men, who may be all employed in war, without the smallest prejudice to industry. From these principles it appears, that slavery in former times had the same effect in peopling the world that trade and industry have now. Men were then forced to labour because they were slaves to others; men are now forced to labour because they are slaves to their own wants.