And I quote:
"And in the mutations of fortune, some slaveholders would be constantly falling into the class of intermediaries and finally into the class of slaves, while individual slaves would be rising. The conscience, benevolence or gratitude of masters would lead them occasionally to manumit slaves; their interest would lead them to reward the diligence, inventiveness, fidelity to themselves, or treachery to their fellows, of particular slaves. Thus, as has often occurred in slave countries, we would find slaves who were free to make what they could on condition of paying so much to their masters every month or every quarter; slaves who had partially bought their freedom, for a day or two days or three days in the week, or for certain months in the year, and those who had completely bought themselves, or had been presented with their freedom. And, as has always happened where slavery had not race character, some of these ex-slaves or their children would, in the constant movement, be always working their way to the highest places, so that in such a state of society the apologists of things as they are would triumphantly point to these examples, saying, "See how beautiful a thing is slavery! Any slave can become a slaveholder himself if he is only faithful, industrious and prudent! It is only their own ignorance and dissipation and laziness that prevent all slaves from becoming masters!" And then they would indulge in a moan for human nature. "Alas!', they would say," the fault is not in slavery; it is in human nature" — meaning, of course, other human nature than their own. And if any one hinted at the abolition of slavery, they would charge him with assailing the sacred rights of property, and of endeavoring to rob poor blind widow women of the slaves that were their sole dependence; call him a crank and a communist; an enemy of man and a defiler of God!"
Slavery and Slavery Chapter 15 of Social Problems, by Henry George (1883)