Here is another origin of the right of slavery, and even of the cruel kind of slavery we see among men.
There are countries where heat enervates the body, and so saps courage that men are motivated to a hard duty only by fear of punishment ; slavery therefore clashes less with reason ; and the master being as cowardly with respect to his prince as the slave is with respect to him, civil slavery is further accompanied by political slavery.
Aristotle attempts to prove that there are slaves by nature, and what he says does not prove it at all.  I think that if such exist, they are those I have just mentioned.
But as all men are born equal, we must say that slavery is unnatural, although in certain countries it is based on a natural reason ; and we really must distinguish those countries from others where even natural reasons reject it, like the nations of Europe where it has so happily been abolished.
Plutarch tells us in the life of Numa that in the time of Saturn there was neither master nor slave. In our climates, Christianity has brought that era back.