I’m writing a low magic fantasy story in which there’s a race of creatures called shadow-thralls that were basically bred as a slave race by a wizard thousands of years in the past. In the present day,they’ve somewhat assimilated into human cities after being liberated, however they instinctively turn to pillaging and raiding if not kept busy. They are weaker and less intelligent than humans. For story purposes, shadow-thralls periodically revolt and begin raiding every few decades until they’re brought back under control and given something to keep them busy. My issue is that I can’t really think of why a medieval society wouldn’t just exterminate them. I need them co-existing with humans for plot reasons, but I also recognize that humans would likely have turned to extermination within the first few uprisings, kind of like how Europeans almost drove wolves extinct or how homo sapiens killed off the Neanderthals. Basically I’m asking what would motivate humans to tolerate a genuinely an aggressive race of “evil” weaker beings and not just genocide them?
Prisoners Dilemma -- They make VERY good slaves.
When we defeated Dire ArchWizard ScaryBad 200 years ago, we took all his gold and treasure. We also took his Shadow thralls. They were created as a slave race. They are still a slave race. Only now we crack the whip.
Our standing army is mostly Shadow thralls. Even though they are physically small and weak they make good footsoldiers because they were designed to fight and to follow orders. So a formation of shadow trolls does not break as easily as a formation of people. Even after it breaks they continue fighting. Our neighbours' have similar armies. Warfare is mostly thrall on thrall.
No one wants to be the first to drop their thrall army and revert to human soldiers. That would take too long and leave you vulnerable.
Keeping the army busy is not too too different from keeping a regular army busy. In Ancient Rome inventing jobs for the generals, to prevent them seizing power, was one of the Emperor's main jobs.
The thralls spend most of their time drilling and training and the rest on large public works. They build fortification and pyramids. They dig cesspools and moats. Sometimes we have a second band follow behind and fill in the moat behind them. This keeps two battalions busy rather than one. They take well to this regimented and busy lifestyle.
Thralls are only allowed inside a town's walls when doing construction. This is where non military people encounter them. The thralls are kept on a tight leash but occasionally one slips out and runs amok.
Exception: Since thralls were originally a slave race of Dire ArchWizard ScaryBad, it is possible for other mages to bind themselves to one or more thralls. This lets the wizard mentally dominate their thralls at range. These thralls are not dangerous unless the spell is interrupted. They are branded with the Wizards initials and allowed to enter the town during daylight hours.
The public is educated with a few tips to deal with an escaped thrall. For example if a shadow thrall enters your house remember to RWAG
R: Retreat into another room or outside the house if there is no obstruction. Otherwise move into a corner. Ideally the opposite corner to the nicest, shiniest thing in the room.
W: Wait until the thrall steals something with both hands. Thralls prioritise stealing booty over attacking people.
A: Approach the thrall when its hands are full.
G: Grab the thrall's left earlobe like Misty and Brock from Pokémon
When you do this, thralls are programmed to submit to you. They will carefully put down whatever they stole and roll over onto their back on the ground. They also release a pheremone that calms down other nearby thralls.
At this point you are legally entitled to euthanise the thrall and the owner has to pay a fine for letting it escape. Or you can choose to bring the thrall back to its owner, and they have to pay the fine to you instead.
They have tried and failed already.
Once in a while the humans decide that enough is enough and try to finish the job after putting down a rebellion. But it always fails for many reasons:
- you have to convince all kingdoms to be fully 100% willing to complete this gargantuan task. If even one tiny city-state decides to not cooperate (secretly or not) you have already failed.
- the extermination is too costly, at some point the soldiers simply cant be paid enough to keep them hunting for the length of time it takes to kill every last one.
- total extermination is a brutal affair, and before it is complete most soldiers desert or ask for different assignments.
- the thralls live in many, many places including in the wilderniss without humans. Finding them all and keeping the bloodlust high enough for years on end is just not feasible enough.
- "what THESE thralls? No these are peaceful hard workers from our village that didnt join the rebellion". As you murder innocent (?) Thralls in more and more villages and cities the population that did care about them starts to rebel against having "their" thralls killed, possibly asking compensation as well.
- pure greed. Enough people who employ them for cheap labor will want to keep them. "Here you go soldiers, all my Thrall work force wink wink money exchange. Execute them over there and dont mention the actual number of thralls I used to have".
You can even make the once-a-generation culling of all Thralls a big thing in your story. People can agree or disagree, cultures could treat Thralls better or worse and even have deliberate cullings to keep the population down against rebellions (which causes the Thralls to rebel even with fewer numbers and makes that culture feel justified).
They do commit genocide at a regular basis. Most kingdoms have orders to kill them on sight.
However, shadow thralls were designed to be expendable minions. Any decent evil overlord would never allow himself to either not kill their minions and not run out of minions to torture and kill out of boredom.
Shadow thralls were engineered to reproduce at breakneck speeds when they are in low numbers. A switch stops this fast reproduction when they have "enough".
This trigger is not understood, but it has to do with how crowded their warrens are and how easy it is to obtain food. Contrary to what one would expect, it is when food is harder to find that they breed the fastest, in order to have enough manpower to gather more food.
Also, crowded warrens split, with a band of shadow-thralls migrating somewhere else. This was encoded in them by the evil overlord so they would expand the mining operation on their own.
So, the shadow-thralls cannot be exterminated, no matter how much effort the kings are willing to spare. Somewhere in the wilderness, a warren will grow, divide, grow, divide, then reach back to civilization.
Exterminating them is a gruesome job that's only done to keep their population in check. They have as much luck wiping the shadow-thralls than killing all the rats and roaches in their cities.
You underestimate the economics of slavery
"Why wouldn't they just exterminate them?" assumes that them being dangerous isn't true of human slaves either, and we've done slavery thousands of times.
Slaves have always been a dangerous gambit, revolts happen, slave masters get killed in their sleep, they require constant policing to stop escapes. But economically speaking, slaves are basically guaranteed to make you rich, all this society would have to say to itself is "would you rather grow your own food and build your own houses?" "Would you rather be as poor as the next town over?" And if, as you're saying, they don't even really need policing as long as they've got something to do, then the cost/benefit decision is obvious.
They don't even need to be particularly good slaves, cult leaders have gotten rich just by having their members doing minimum wage labour making novelty pens, as long as you don't have to pay people beyond building them a house and feeding them, things they would do with a larger portion of the money you would've paid them anyway, you keep the difference and can sell product cheaper than any competition.
and your town can perfectly mentally justify this slavery because, as you mentioned, they get restless unless you give them something to do, so they see themselves as parents to a child race.
Honestly slave races are a kind of offensive idea for obvious reasons, but if they're going to exist, you've pretty much already made an ideal one, it doesn't need more justification then you've already given it, people might be worried about the occasional revolts and violence, but that's true of real slaves, the culture will simply adjust and build structures for maintaining the status quo.
1:Greed, As you said they are less intelligent then humans... so cheap labor could be a reason why the upper class (who is relatively safe due to personal protection) could use them as a labor force, so what if they kill a few customers here and there?
2: Display of power, a (religious) group could want to keep them alive and revolting to make the people scared so that they themselves can remove that fear by having a standing (holy) army to fight them if needed...of course this army needs to be funded so say hello to taxes.
3: Culture/Religion, their main religion might highly frown upon killing innocents, people have done stupider things in real life based on their faiths.
4: High reproduction, they might breed so fast that taking them out permanently requires more effort then it's worth (perhaps due to internal conflicts between the parties that have to unite to actually exterminate them. As you said they ere bread for war so a high reproduction number in a short time is something the wizard might have planned for.
Your mistake in the question was the word "cities". The medieval world didn't have cities, not at the scale we'd understand today, and people didn't go there to assimilate. Medieval cities were only large towns, really, and not many people lived there.
For the other 99% of the population, farming was the thing. And this is where the shadow thralls come in, because there is no such thing as a medieval farming economy with too much workforce. The more hands you have (in the absence of machinery), the better you can farm. You don't even need to develop the horse collar, because you have teams of thralls who'll pull the ploughs. You basically have the perfect slave economy, because unlike slaves they're unable to think about rebelling.
Roads and other public works
In the meantime too, the king and his lords also have thralls. When they aren't fighting someone, they can be solving the biggest problem for the medieval world, which was how to get soldiers around quickly. That's why all major roads in all medieval states existed. Thralls would be perfect for the grunt work of roadbuilding and maintenance. And then of course the country gets the economic benefits of traders also having roads to get goods around.
Or city defenses. It took years to build defensive walls, and it took people out of farming to do it. With a strong farming economy, you've got plenty of food left for the local lord to put a team of thralls on that.
In a medieval context, you simply can't overstate the degree to which the available man-hours of muscle was the limiting factor for development. If you've got extra muscle, it'd absolutely get used. No doubt some states would go down the "slaughter" route instead though - and they'll be crushed economically (and probably also militarily) in pretty short order.
Have you ever heard on the NYMB (Not in my backyard) syndrome?
It's what happens when we want something, just not close to us. Like we want industries, but not close to where we live.
Same here: a genuinely and aggressive race of “evil” weaker beings is a good thing when it's busy in an enemy land, it's a bad thing when it's in our land.
So, war is the reason why such creatures are not driven to extinction: they are too useful in war to be taken permanently care of.
Sounds very interesting! So, they're created as a slave race. Perhaps they have unique skills that make them invaluable.
I don't love cats. Not as pets. I find wild cats interesting. But generally speaking, I don't want cats anywhere near my house or slaying local biodiversity: baby birds, mammals and all these other wonderful creatures I prefer to cats.
However, I lived for a while in my mum's renovated shed, plagued by mice. I had no food in my shed or any traces of it and there was nothing I could do to keep them out. I could set traps and kill a few of them, but there was an inexhaustible supply of the little buggers and they kept me awake, shat everywhere and occasionally I'd wake up with one climbing over me.
I soon moved into a bedroom in an old house with holes between the floorboards and hundreds of wonderful places for mice to live and eat and survive. Except that the house had three cats and in my entire time there I never saw the traces of a mouse. So yes while I don't love cats, I prefer them to a mouse infestation. I was pretty unhappy when one of the cats pissed in my room once. But overall I preferred cohabitation with these cats than with the mice.
What I'm suggesting is that while shadow-thralls may be less intelligent than humans, they might be better at something than humans. I'm smarter than cats are, but I can neither hunt mice or deter them from inhabiting my abode. I would keep cats around sooner than let my home be overrun by mice. Maybe shadow-thralls are a form of pest control.
It's convenient for the leaders to have a periodic, predictable, easily handled threat that seemingly threatens society but is otherwise a useful workforce the rest of the time. It helps maintain those in power and promote cohesion.
Also, everyone loves cheap labour.
My first thought was "elephants". In some countries, they are simply pests -- like having gigantic deer that eat human crops, encroach on human lands, are a danger to humans and livestock and were well on the way to being killed off. What stopped the genocide of elephants? They became a cash crop, mainly from hunters willing to pay extraordinary fees. By carefully selecting what the hunters can hunt, and where, and how frequently, the nations that have these elephants have turned them from a pest to a source of income powerful enough to convince them to expand elephant reservations beyond the original conservation agreements, willfully pushing back people to make room for more elephants.
The takeaway is you just need them to be useful (and manageable) in such a way that despite the problems of them being pests to society, their value is too high to get rid of them.
Maybe, for example, there is a tax on shadow-thrall ownership which goes into a "shadow-thrall management" fund which keeps things pretty well in check. People gladly pay the tax because the thralls always pay for themselves several times over. If things start to get out of control, there's already a crack team of full time Rangers whose only job (paid for by the taxes) is to deal with it, so the general population is rarely bothered.
Even on Earth, genocide tends to be frowned upon. Now picture a fantasy scenario in which folks may actually have visited Purgatory, and you can imagine that almost nobody in that culture is too eager to sign up for a million laps around the Mountain of Thorns with their eyes sewn shut.
Even beyond selfish considerations, their mages can commune with the thralls. For precious hours, the curse can be lifted entirely, and anyone can converse with the shadow-thralls as entirely normal, sensible people. They can see how the bad magic comes back, bites into them, and makes them do bad things.
The combination of fear and pity leads the unaffected people to be compassionate and understanding. When the shadow-thralls start beating them up and breaking things, the normal people try to remember this is their chance to cultivate a ticket to the Elysian Fields through forgiving behavior. When the mages put down the revolt by gentle means, it gives a new generation of thinkers a chance to try to finally understand and break the curse once and for all.
Of course, for certain wizards it is also their chance to try to finally understand those long-lost secrets, and to prepare their plans to enthrall all of humanity...
Do commit mass genocide. Do it periodically enough to prevent the shadow-thrall population from reaching a number that would let it overpower humans. However, you only kill, say 30% of them and make it a mandatory thing. Do the population control during a thrall census so that owners can’t cheat and add massive fines for not taking thralls to the census. Just make sure to keep, give or take depending on your population of humans and thralls, 100 or so breeding pairs of thralls in which to replenish the stock. I’d say that you shouldn’t let the thrall population be more than 70% of the human population (resource loss and overpowering humans is the main reason). Also, make them were shock collars set to lethal force to prevent rioting. Don’t have to take this idea, but I reckon that it would be a cool way for a rebel group opposing this structured genocide to pop up.
Let history be your guide and make them equals
I'd steer clear of the weaker, less intelligent inferior slave race idea. Instead it sounds like what you want is an equal but different war-like nomadic people that gives your country serious challenges with periodic raiding activities. Then look to historical examples and adapt them to your purposes. One example that comes to mind is the interaction between the historical nomadic Scythian people (not to be confused with the later misuse of this name) with the Persian empire (e.g. the Wikipedia article is fascinating). In general nomadic raiders can give a static empire real headaches and be surprisingly challenging to conquer. But again, I'd make them equals and not an inferior slave race. Your story will be better for it in a variety of ways.