This is the rant on slavery.

1) What kind of slavery does your fantasy society have?

Slavery might exist for many different reasons in a fantasy society. The usual kind is (apparently; see point 3) the kind that existed in the United States, Brazil, and the Caribbean Islands until the nineteenth century: chattel slavery, under which people were treated and regarded as property, and the condition of the parents could be passed onto the children without qualms, and slavery itself was sustained by certain mechanisms of coercion and thought that helped perpetuate slaveowning among the ruling class. However, that isn’t the only kind that has existed.
Other possible kinds of slavery in a fantasy society:

  • Debt slavery. Does someone in the fantasy world borrow money and then fail to pay it back? Does he default on a different kind of debt that he owes social superiors, or a neighbor, or someone else? Then he may be seized and made to work it off, or perhaps his family could be sold into slavery to pay for it.
  • Crime slavery. Slightly different from debt slavery, this would be more like forced prisoner labor—a much more common threat in fantasy than anything actually portrayed.
  • ‘Foreigner’ slavery. Perhaps, for whatever reason, the only way that people of another race, species, or nation can enter a particular part of your fantasy world is as slaves. Eventually, they may be able to buy themselves free and become respected members of society. This kind of slavery would not pass on from generation to generation.
  • War slavery. Prisoners of war could be made into slaves, servants, adoptees, or sacrifices among nations such as the Aztec in North, Middle, and South America.

Frankly, most of those systems would add some variation to the usual fantasy idea of chattel slavery, which many fantasy authors not only choose to portray, but portray without much competence (point 3 again).

2) Decide if your society is a “society with slaves” or a “slave society.”

This is a useful distinction that historians have come up with. A “society with slaves” is a society in which some people have slaves, but they’re not fundamental to the economy; they might exist side by side with indentured servants, free but poorly-paid workers, slightly more important artisans, and mechanized (or magic-ized) industry. A “slave society,” on the other hand, is one economically dependent on its slaves, probably because its staple crop, say, is not one that most free people would willingly tend and harvest, or because whatever must be done to earn money is difficult and dangerous. The profits tempt people to keep on doing it, but on the other hand, they want to live and spend their money, not die. So they’re more likely to take slaves and then to make them so important to the society that the temptation to stop slavery becomes slim to nonexistent before the threat of what would happen to their money. The harvesting of sugar cane in the Caribbean islands, at which the majority of slaves died, is a prime example of this.
This will make a difference to the way that you portray slavery in fantasy. I’ve read a lot of fantasies where slaves were common and not really questioned, but they also seemed incidental to the economy; in fact, sometimes I couldn’t really tell why they were there at all (see point 4). In others, slavery was seen as wrong and the heroes had to convince other people of that, but the owners seemed to just give in and agree with them without much thought of consequences, or to oppose them for silly reasons (point 4, damnit). Slavery should make just as much sense as anything in the fantasy society. When it is flung in, I think it’s to serve a different purpose: not to make sense, but to provide objects of pity or an easy moral issue to attack. Writing fantasy should be difficult, complex, complicated, nuanced, detailed, a struggle, a joyful battle. Make sure to explain and integrate slavery into the society.

3) What leads to the dominance of masters over slaves?

In some fantasies, the author writes about slaves living in fields, barely getting any sleep or food, enduring difficult and dangerous tasks—working out in the hot sun seems to be a favorite—enduring beatings, and so on. And the big question in my mind is:
Why don’t these people just run away?
Seriously, in some fantasies there is not an answer. The slaves suffer horrible treatment, and they know it’s horrible, and they hate it. Yet they make no attempt to do anything but go along with the masters. That’s because they have to wait for the Wonderful Hero to come and rescue them, of course, but that’s not a good reason. Look into the minds of slaves and see what keeps them there.
In the case of chattel slavery as it was practiced in the Western hemisphere, there were many psychological and social and legal constraints as well as the ever-popular whip and club. The concept of race was used to keep lower-class whites feeling superior to blacks (and Indians) and divide them from uniting with them and rising against the higher class. (There is evidence that before upper-class whites hit on this tactic, white indentured servants and black slaves did unite, fight together, make love together, and make common cause in other ways). Draconian slave codes threatened such punishments that the anticipation of them, far more than the actual infliction of them, kept many slaves quiescent. It helped enormously that the slaves were usually visibly different, of course. The mixing of slaves from different backgrounds and languages isolated them and destroyed the sense of belonging that they would have had in their own homelands. And in places like Barbados, the work was exhausting and dangerous enough to not leave that much energy for rebellion. That’s only the barest part of the mechanisms of coercion, of course, but it’s enough to give you an idea.
This doesn’t mean slaves never struggled against the constraints. They did. They could pretend to be sick, to be hurt far more than they were by a whipping, to be so stupid that they couldn’t understand what was required of them. They could work so slowly that almost nothing got done. They could steal small things to inconvenience their masters and make their own lives better. They could at least attempt to conduct their own ceremonies, such as funerals and weddings, so as not to let their masters control every aspect of their lives. And they could and did run away, despite the risks and dangers of that. The temptation was stronger if there was a friendly place nearby; Spanish Florida was near British South Carolina, for example, and offered freedom for any slave that got that far. Not many of them made it, but that didn’t keep them from running.
So consider reasons that your slaves don’t run away, other than physical constraints alone. And consider ways that they could rebel, not only including but up to an actual revolution (see point 5).

4) Why do these people need slavery, anyway?

Really, I don’t understand why some authors use it. All right, so the evil nobles have slaves. But why not servants? They might have to pay servants, but not that much, and servants often didn’t have much more choice than slaves in a pseudo-medieval society; they can’t leave easily, they’re dependent on their masters, they can’t show open temper or rebellion without being punished, etc. Slaves are dangerous in a way that servants can never be, because they can decide that they would much rather hate and hurt and kill their masters than go serve in another place. They can’t go serve in another place. They’re backed against a wall. Back them far enough, and they’ll lash back.
Additionally, under chattel slavery, slaves make their masters incredibly paranoid. The fear of slave conspiracies was constant, from Barbados to Jamaica, from South Carolina to New York. Slaves were rewarded with their freedom if they brought the rumors of a conspiracy to their masters’ ears. When masters became convinced that their slaves were plotting against them, they didn’t hesitate to use torture, execution, and punishment they wouldn’t ordinarily have, for fear of damaging valuable property. Fear is a constant companion in a society with chattel slavery, on both sides.
So really sit down and think about why you have slavery at all. You may have a society with slaves rather than a slave society, and you may have a system other than chattel slavery, but it still needs to be thought about.

5) Portray all the difficulties in a slave rebellion.

This is another consequence of fantasy authors wanting things to be easy for their heroes, I suspect. The hero talks to a few slaves, gets them outraged, talks to a few others, and suddenly the world is different and the hero is accepting congratulations from everyone (or being crowned, maybe).
In our history, there was only one successful rebellion purely among slaves: the Haitian Revolution. And that took 13 years (1791-1804), and involved double-crosses, steps backward and forward—France did abolish slavery for a time, and then Napoleon reinstated it—and the deaths of hundreds of thousands of people. It also went mostly unacknowledged by the United States and Europe, though it did inspire revolutionaries in other countries, like Simon Bolivar.
If you have a well-worked out system of slavery and a society to hold it up, then you have set yourself an enormous challenge to portray a realistic change in slavery. I think this could make an enormous story, at least as sprawling as the average fantasy fight against the Dark Lord, and a lot of heroes, villains, and characters who transition between both. It’s really in your best interests not to just wave a magic wand, literal or figurative, and clean the mess up.

6) Don’t portray slaves as happy to serve their masters.

This is a variation of what I talked about in the servant rant, but it applies with peculiar force here, because authors seem to have a tendency to depict slaves as wise, patient, and happy to serve the whims of their masters, because they love them. Or something to that effect.
Tell me: if these people are willing, why are they slaves? Why aren’t they free servants? (Point 4 again). Why would a society really need a system of slavery if there was a whole group of people willing and eager to serve the dominant group, or if being of a lower class somehow magically transformed everyone into that stereotype?
Slavery takes away freedom. It might be in accordance with laws, like debt slavery; it might be something that the people in the slave position accept with stoicism rather than rebel openly against, such as if they’re prisoners of war and expected to be taken slaves if they lost. But they still didn’t make the choice to perform domestic work, scrub their master’s floors, tend his fields, or whatever else you have them doing. They didn’t make the choice to have all the constraints heaped on them that they do, and I haven’t encountered a fantasy author yet who could convince me that to a slave, that was somehow just an acceptable price next to the joys of serving the master.
That doesn’t mean relationships between masters and slaves are completely simple. There’s point 3, about the many small ways that slaves could rebel. There’s also the choice made by authors like Carol Berg, who portrays a system of chattel slavery based on racial and magical difference in the Rai-kirah saga, and yet avoids having the slave narrator, Seyonne, be either a helpless victim or a cheerful and grinning stereotype. He reluctantly takes up the task of protecting his master, Aleksander, against demons because that was what he was sworn to do before he became a slave, and he still considers it his sacred obligation. That being enslaved took away the magic he would ordinarily have used to perform the task is a further, cruel irony. Berg never forgets the cruelty, and slavery is not happy in these books.
There are very few things in fantasy that cannot be improved by being made complicated, and the relationship between master and slave is another of them.
Not sure what rant should be next, really.