Slavery (n.) is an economic category, one of the great importance even in the modern era.
Slavery (n.) cannot be fought on its masters' terms: to demand its abolition because the slaves' rations cannot exceed a low maximum is the logic of a rebel slave still in thrall to them.
Slavery (n.) ties up capital uselessly: the slave's price is only his future surplus labour capitalized in advance, money gone that helps the owner exploit him not one bit.
Slavery (n.) can be bought into with money, but money in the buyer's hand never made a slave: the sale presupposes the slave, as the wage presupposes the propertyless worker.
Slavery (n.) lies latent in the family and grows out of it with population, wants, war and barter.