Why would they use human soldiers over undead ones?

Question

In my setting you can revive people from the dead as long as the brain is intact, though you have to remove all their organs and replace them with a suitable alternative Egyptian mummy style.

The Technology level is late Bronze Age - early Iron age roughly. Think Ancient Assyria/Persia/Greece where they use Bronze for some things like armor and Iron for most everything else. For now just assume no other magic exists. Most armies in the setting use 'supply depots' à la the Neo-Assyrian Empire.

Whilst they're dead though you can whisper commands into their brain and when revived they will follow that command.

If you don't do this however, they just come back normal with some memories deleted.

They can also feel what killed them for the rest of the time they exist and they will continue to exist until something kills them. Example: you stabbed them in the heart, and when they get revived, it feels like a dagger is embedded inside them even when there isn't and there's nothing they can do about it.

They're not any more fragile than normal humans other than the fact they can't heal from injuries and can't feel any physical pain whatsoever besides whatever killed them (still emotional pain though, since that's mostly mental health stuff) and in some ways are more resilient (don't have to breathe, don't have to consume things, can't bleed)

So my question is, why would the powers of this world ever need to use human soldiers that might mutiny and have needs like breathing and eating over undead people?

Answer 1

The undead make TERRIBLE soldiers.

If you give them commands, they will obey them mechanically, even when it produces disaster. Direct one to bring in water, and it floods the house. Direct one to set a fire, and it burns down the city.

If you don't, they are in pain. They would not obey YOU, you are the source of their pains, and it's very likely they will attack the source of their pain. If not, they will want to die, from the pain. A belief that the undead are unnatural would also inspire them to die as quickly as possible.

Answer 2

from OP:

(still emotional pain though, since that's mostly mental health stuff)

The mental state of soldiers is key to victory.

The undead are in a very bad place, mentally. They have lost everything they had - they cannot go back to their families because they have become monsters and they cannot hope for some normal life after the war. They hurt, all the time, and physical pain adds to mental anguish. They are not concerned about being punished for disobeying. They cannot be hurt any more than they already are, and they have nothing left to take.

The original Robocop did some things well and this aspect was one of them. The Robocop has been brought back from the dead via technology. In one scene he sees his wife and child. He can remember what he used to be, but they do not recognize that.

War is bad enough for human soldiers, who can sustain their mental state with whatever inner strength or hope or faith or support they might have. Your undead have lost nearly all of that. Those who are motivated by patriotism will soldier on. Some few find strength in the company of their kind. The rest of the undead soldiers routinely commit suicide within a week of being raised. Are you going to raise them again?

Answer 3

They Spook The Horses

Horses and most other large quadrupeds (camels, donkey's etc) don't like being around corpses. What's more in this setting, they REALLY don't like being around walking corpses. Maybe the necromantic magic spooks them, maybe they can just sense the unnaturalness of a mummy wandering around. Either way, an army with too many undead in it cannot keep horses or other beasts of burden close enough to camp to be useful to the army. Cavalry is out (if it's been invented yet) chariots are out, oxen to pull supply wagons are out. Because if the things smell/sense the undead they break all restraints and bolt.

Sure they also spook the enemy's horses, but the downsides of lacking your own don't make up for it. (The enemy is more mobile, has better scouts, and has better logistics even if your all-undead force mitigates their cavalry/chariotry in actual battle.)

Don't overlook the logistics. Even with "supply bases" moving an ancient army was TOUGH. Especially for offensive warfare when you'd obviously be operating away from your own supply bases. Undead might be great for fortresses (can't be starved out, simple commands suffice for guarding fixed positions) but in open warfare an army without them is going to have the advantage.

An undead army such as you describe still needs a logistics train. They don't eat, which is a big bonus. But they also still need replacement weapons, spare ammunition for slings/arrows, potentially siege equipment, and all the food and usual supplies for whatever humans are in charge of them. Without horses/oxen/camels they're carring all that crap themselves. Which is terrible because it puts more wear & tear on the corpses. The army might start off quicker than a "human" one (they can march farther due to not needing breaks for food/sleep) but they quickly slow down as knees blow out, joints degrade, muscles shred themselves apart etc etc etc. So most armies use human or majority-human troops in most circumstances, and use undead forces as small formations of "gimmick" troops to protect against enemy cavalry in the field, and for guarding specific strategic chokepoints within the kingdom during defensive wars.

As another aside, there may also be a strong religious component to not wanting a ton of these guys roaming around. If they feel what killed them, people are gonna be MAD if you turn their relative into undead infantry. "My father constantly feels the pain of his death instead of experiencing his peaceful/blissful afterlife like he SHOULD BE DOING RIGHT NOW." Having a bunch of these guys would be a sure-fire way to make most of the populous hate you.

Answer 4

A semi-scientific approach : Undeads don't last long

You said that undead individuals cannot heal their injuries. The thing is, the healing process in living beings is done constantly, at micro-and larger scales. Indeed, a lot of cells die in our body every second and new ones are created. Only a few things remain intact over the lifespan of an human.

Now, undeads are mummified to slow down the decaying process, but the thing is, mummies are actually quite fragile, especially if you send them in mud and dirt, taking sword hits from their enemies. All of these misfortune events will lead to open or wet tissues, a good fertile ground for all sorts of parasites and bacterias which will devour the body from the inside.

Even if they manage to survive the battle, you'll have to thoroughly disinfect and knit back all the damage done, which would require almost as much mummy handlers as you have injured undead soldiers. Because unlike some humans, any scratch done won't repair themselves -even partially-. And since undead cannot feel pain, you'll have to do a full check-up yourself, because you can't simply ask "where is your pain?".

Note that being able to feel the cause of death in your body will surely feel mentally distressful at best, and like when you have that nasty itch you can't get rid of, you'll feel the need to scratch it, removing any protective ointment you'd have there.

Not taking account any kind of muscle atrophy and rigor mortis they'll have by being mummified, I think you'll get a single usage soldier who'll last a good 2-3 weeks and with regular maintenance, which is very short for a medieval military campaign.

Answer 5

A dying man is not a good soldier.

I have no firsthand experience, but I imagine dying can be rather traumatic and painful, particularly if you're in a violent period of ancient warfare and limited medical science. The knife in the chest that killed you likely hurt a lot, to the point where you couldn't focus on much else. Every single member of your undead army must experience the pain of their own death at all times, vastly diminishing morale and combat effectiveness - they mostly just scream and writhe around in pain, waiting for the sweet release of death that will never come.

A dying man is not a good soldier, and you have an army made entirely of men who are moments from death (or at least that's how it feels to them). At the start of any battle, all of your soldiers are already mortally wounded!

Answer 6

In general, the "don't need to eat" part makes undead vastly superior. The hardest part of war, especially in a medieval setting, is generally logistics.

Therefore, undead need a major flaw to justify not using them for everything.

Idea 1: magic

There is a special kind of magic that is very efficient against undead in certain situations, and doesn't affect the living.

• Maybe holy magic.
• Maybe interfering with the revival spells allows a caster to disable undead.
• Or reverse the idea: maybe some spells that are extremely useful for war (healing magic? reinforcement magic?) just cannot be used on undead

Idea 2: they are costly

Undead are just too costly to create to make an army out of them. And when they're broken you cannot revive them anymore.

• corpses in too bad a state cannot be used (you can make undead out of them, but they are basically useless in combat), so you have to procure good corpses (you cannot just pick them up on the battlefield)
• the undead-making process requires a powerful caster, expensive ingredients, and a lot of time

So the use of undead is almost exclusively reviving extremely powerful individuals / making chimeras out of different body parts, because that's the only thing that justifies the cost. There is a market of powerful dead bodies.

Idea 3: they have a short (un)life expectancy

Since undead don't heal, the accumulate wear. Every small bruise will stay, and with time, they accumulate. Their body wears down, unable to repair itself, until it becomes unusable. And in the rough environment of battle / military camp, it can be fast. That back problem caused by sleeping on the floor never heals. Worse, since they don't even notice it, they don't try to mitigate it, so it worsens.

This reinforces the fact that undead are expensive, since you have to replace them frequently

Answer 7

Moral/Ethical/Cultural reasons

The act of reviving dead people is considered immoral by the society. Families would not feel comfortable with reviving a relative to send them to war, specially if their relative is going to be both brainwashed and feeling constant pain of whatever they were killed by.

Using this as one of your restrictions, whoever is recruiting undead would have to work with bodies of people that:

• Actively declared that they would want to be revived as a soldier. (No brainwashing would be needed)
• Do not have anyone close to them, like family or friends, that would be against their revival.

This makes an army of only undead soldiers too small to be used. Maybe a mixture of both human and undead would be the best, depending on whatever operation. Also this would mean that the human soldiers could keep in check any undead that was revived without being brainwashed.

This answer considers that whoever is making this army, cares about the morality of what they are doing.

Answer 8

Humans are far superior to undead

To take a freely inspired line from Star Wars. Humans can think more creatively than undead. They can respond quickly to unexpected outcomes or situations. They more easily can reevaluate a plan, or set a new goal when a previous has finished or is no longer valid/should receive less priority. They also aren't distracted by pain or memories. They can fight with more vigor and are more likely to engage in self protecting behaviors, giving them more chance to survive.

They are also the only ones that can procreate. Although you can then use the dying people for the undead army, they do seem to cost much more than a human. A human can add their worth to the economy at all times and the parents carry most of the upbringing costs. The undead require a lot of upfront costs from the government. The same can be said for humans with training, but undead soldiers might need the same and possibly more.

Most likely they will get one or a pair (redundancy) of humans with every squad of undead. Still, their seeming high upfront cost and utter reliance on commands is a big weakness. The large scale can be compared to a non-autonomous robot fighting a boxer, where you need to quickly give new orders to the robot with every move of the boxer. Reactions are slow, uninspired and basic. Not to mention that they might be taken over by the opponent if they somehow can budge in and start whispering in the ears.

To make properly use of an army of undead, you'll probably only revive already trained people that can rely on earlier training, together with humans close by to give them orders.

Answer 9

Limit the number of your magicians... for reasons.

A line in your question (Whilst they're dead though you can whisper commands into their brain and when revived they will follow that command) made me wonder this...

How many magicians have the ability to create your version of the undead? It creates a problem if you have five magicians in a given Empire, but they need to create an army of 5000 asap. That would be 1000 undead for each magician, and that's got to be taxing, even if the magic is easy to do.

But all "believable" magic systems have a price to pay of some kind, so what would be the price to pay if you had to create that many undead? High I would imagine.

So what would make living soldiers preferable to the undead, given the undead's advantages? The magicians to create them are A) hard to find because so few have been taught this awful dark magic, B) the spell to create each undead takes a while; you cant just do a blanket spell to create an entire army all at once, and C) so few magicians have been taught this kind of magic because its very taxing on the magicians themselves.

Taxing how? Maybe it steals some life force from the magicians? Maybe it takes time off their lives? Maybe they get terrible wounds all over their bodies when they do the spell? You'll come up with something.

(Why would a magician ever want to do this? Power? Glory? Money? They were seduced/coerced somehow? Again, your call.)

So maybe, your undead are better as smaller special ops type groups, or even as assassins, rather than entire armies. Just a thought.

Answer 10

I'm assuming a best-case scenario and only undead that died a nigh on painless death are recruited.

In warfare we have this idea of masses of people dying all the time. A single slash across a steal plate armor and somehow that person is dead almost instantly!

The truth is that most fights there are very few directly dead, even if you are on the losing side. Most will die of disease and infection after a battle rather than during the battle. Pre miss Nightingale* this could be more than 10x the number that died on the battlefield or from their wounds directly afterwards.

At this point you say "ah but my undead can't die from infections! So they would be superior!". But the key here is that the undead cannot heal. If your medieval people have their own Nightingale who teaches them antiseptics and hygiene the death toll of disease can go down and many soldiers can become healthy enough to fight or go home and do jobs.

Your undead will keep all wounds. They will not succumb to disease and infection but they will not improve their condition either. That means that every battle you increase the pool of undead who become increasingly useless to your empire. Why would you rule an empire of undead with slashed bodies if you could let those undead do the farming, supplies and other jobs required to keep an army going? In the passed entire armies were disbanded for periods of time to make sure those people could help with harvests, then re-enlisted/conscripted later on. Your undead are the most valuable workforce you can have to support your living. Use them as such!

*https://en.m.wikipedia.org/wiki/Florence_Nightingale

Answer 11

Life force obeys all applicable natural laws of conservation:

1. It is finite: Life force is the essence of each living being, and can only be created naturally, through procreation.
2. It must come from somewhere: The spell is impossible to activate without the input of life force.
3. It must come from other living beings: There's no way to produce life force from machines, agricultural sources, natural forces, or anything except other living beings. It also cannot be obtained from someone who is already dying, or who is fatally wounded (unless that's how the ritual works).
4. It functions only on a 1:1, all-or-nothing basis: Another living being must perish in order to raise a dead being. It is not possible for groups to sacrifice partial life force in order to raise one being from the dead.
5. It is strongly typed to specific species: Only human life force is compatible with raising humans from the dead. Only elephant life force is compatible with raising elephants from the dead. Only frog life force is compatible with raising frogs, and so on. Any substitution of other life force produces disastrous results.

The natural laws of conservation introduce the element of scarcity or finitude, and reduce the number of times undead soldiers can be raised. There's no way to raise an army of one million undead without taking one million other lives. The greater the size of an undead army, the greater the waste of life from others, be they farmers, miners, craftspeople, babies, or any other group.

Thus, if a ruler wishs to create an undead army, it comes at a significant moral and ethical cost. It requires a ruler or general to commit (or to sign, or obey orders for) some kind of atrocity that will not go unnoticed, even among their own kinsfolk or countrymen, or other allies.

Answer 12

The way you've describe your undead, I imagine that many (if not all) would be extremely resentful over having been reanimated: constant pain and disfigurement, unable to enjoy the pleasures of life, etc. Because of that, you have the "djinn in a bottle" problem: a mean-spirited supernatural being who will follow your orders technically, grudgingly, and to the letter, but will happily muck things up as it suits his mood or sardonic sense of humor, just to make your life miserable. If you're lucky you reanimate someone who really dislikes your current enemy, and is happy to fight them for a while because it's what he wants to do (but what happens when he gets sick of doing it?). If you're unlucky, you reanimate someone and tell him to go kill the enemy, and he instantly turns and tries to lop your head off because you didn't specify whose enemy he should kill.

Human armies run on loyalty and pride. Living humans love people and things; they want to protect them, and show how valorous they are in the process. That makes them dedicated and reliable. An army of resentful, malcontent undead might make good cannon fodder, but they have no reason to be loyal to your cause.

Answer 13

Only a few undead soldiers can keep their sanity for an extended period of time

You state this:

They can also feel what killed them for the rest of the time they exist and they will continue to exist until something kills them. Example: you stabbed them in the heart, and when they get revived, it feels like a dagger is embedded inside them even when there isn't and there's nothing they can do about it.

This means that your undead soldiers are constantly in pain and are forced to relive the moment of their death every moment of their undead existence. Chronic pain is a very debilitating condition that leads to a number of negative symptoms. Anxiety and depression are some of the most frequent ones. Untreated chronic pain will also trigger detrimental changes in the brain that will lead to lower combat prowess due to lower control over the body and reduced cognitive capacity.

A constant reminder of the event that led to one's death, especially if death is unnatural, would also have a negative effect on mental health and increase the likelihood of PTSD-type disorders.

Your world does not have the knowledge and technology to deal with chronic pain and mental disorders. And even if it had it would be economically non-viable to keep an army of undead that need to be in psychological/psychiatric treatment in addition to daily medications.

Perhaps, some of your undead managed to live to a ripe old age while keeping their wits about them and being rather healthy. They might've died peacefully and do not suffer from any pain. However, these will be the minority due to the technological limitations of your world. I am not sure how your revival magic works, but if it does not bring people back in their prime condition, old people would not make could soldiers due to the limitations of their age. You can, probably, train them for non-combatant positions, though.

Answer 14

The Undead don't know when to hold 'em, don't know when to fold 'em, don't know when to walk way, and don't know when to run.

Human soldiers fleeing a battlefield is usually not a good idea, but there are situations where it might be useful for your human soldiers to flee a battlefield and let a commander know when a situation has changed dramatically not in their favor.

Take, for example, sending some troops across a mountain range, over a plains biome, and across a bridge to try and attack a force on the opposite side (i.e. a city territory, a set military barracks, etc.).

The other side might setup a few troops on their side of the bridge as scouts, and when the Undead start to cross it, allow them to, in part - and then destroy the bridge.

The Undead on the other side of the bridge might then try to walk across or use undead bodies as a bridge to cross over, but they could be susceptible to Greek fire in the river between the bridge, or just being pelted with arrows as they attempt to do that.

While a set of scouts try to also take on the undead that have successfully crossed the bridge, or just let the much smaller force try to take on the barracks or city. If they allow 10 Undead at a time to try and attack the barracks, it doesn't matter if you send 100 or 10000 Undead soldiers - 10 Undead at a time is presumably manageable for the opposing army, barring them automatically resurrecting on the site as they die.

If this was a human force of soldiers in the same situation, the soldiers crossing the bridge before it was destroyed may respond to the destroyed bridge by surrendering, or fleeing to the mountains, while the side that hasn't yet crossed the bridge may provide covering fire for them or begin fleeing themselves, perhaps back across the path to the commander to report on what happened. They may also setup camp outside of the river area while sending a smaller scouting party back to ask for reinforcements or bridge building capabilities, or additional orders. If they encountered the Greek fire and had no existing knowledge of it before, they would also want to relay that back.

Similarly, if they encountered Greek fire while on ships, humans would understand that not only are their lives important to get back, but so are the ships that were built - especially if it was followed up by catapults throwing rocks at them to try and sink them. Some orders are given with a bad understanding of the situation.

Additionally, you can give a human force - especially a human commander - enough information about their task that they might catch on to information that indicates that the information higher command has is incorrect, or a possible trap, and update them as necessary. For example, if you send them to take on a large group of the enemy army force to keep them away from a castle you're planning to siege, and they show up and find only 90 soldiers holding up the outpost instead of the 900 you thought were going to be there, a human commander might fight the 90 soldiers quickly, but also send a messenger back to alert their high commanders that their information is presumably out of date; there's a discrepancy in the force they were told to attack and the force that was there. Useful information if you have a mole in your team providing false information.

Finally, humans will likely retreat if they feel that the enemy army is starting to encircle them, or attempt to force them into a worse situation. The Undead may still want to fight the enemy force, because that was the order they were given, and they may not have gone to war with the enemy force if they weren't compelled to anyways.

Furthermore, the Undead have no inclination to prevent the enemy forces from killing them and resurrecting them against you.

If your Undead fail to successfully defeat the enemy and instead get themselves routed, then now the enemy has a full group of soldiers they can resurrect and send back against you. As a bonus, they're already equipped with all the equipment they really need.

You did equip the Undead with armor and weapons, right?

Your human soldiers, upon realizing they may be in a losing fight, and that they may be resurrected as Undead, and may deliberately either flee to make it harder for them to be resurrected, or get themselves stuck under crushing buildings or rocks, or deliberately try and break and destroy their lances, swords, and bows, such that they can't be used against their allies. At the minimum, they can start denting their weapons on purpose. Not ideal, but they can try and avoid giving an advantage to the enemy - maybe they cut off their sword arm just before dying, or their legs, or both legs and arms in a final act of defiance.

Answer 15

They cause unrest

In ancient times, empires often relied on expanding into new lands(usually by force) to keep their coffers in the black. Another answer has mentioned your own people objecting to the practice of raising the dead; unsurprisingly so, given mankind's longstanding views and taboos regarding the dead. In your own core territories, this a less of an issue since there you have a much stronger ability to influence people's views. But what about people in the newly annexed frontier? Dissent engendered by the presence of undead soldiers there can cause a very costly problem.

They can't multiply

After your armies have carved out a swathe of land for your Necropotamian Empire, you naturally want to hold on to the land. Emperors often rewarded soldiers who fought and bled(figure of speech when undead are involved, I know) for the empire with tracts of land parcelled out from the new frontier. This is one prong of a greater strategy to bring these new lands fully into the empire through ties of blood, culture, and trade. But if your troops are undead, they can't go forth and multiply. They'd lack the necessary apparatus.

Answer 16

"Whilst they're dead though you can whisper commands into their brain and when revived they will follow that command"

This makes it troublesome to field an army of the dead in a fluid situation such as war. Let's say you've raised an army of undead and whisper commanded them (prior to revival) to travel to the great plains, where there is a major battle taking place, and destroy your enemies. Since they have been whisper commanded they have an undeniable urge to do just that and they head that way, but while in route the enemy fled the plains and went to the forest. This is where the problem lies: the undead don't have the urge to go to the forest, they just mingle about the plains where their urge takes them.

Living human armies can adapt easily to the same situation and have their orders changed as needed.

But where the dead excel

Is during a siege. You show up with 1000 men and besiege a castle, 2 days later you have had 100 men killed yet you can still field 1000. 900 living men and now 100 undead with a stop at nothing urge to get inside the castle.

Answer 17

I like to think that they wouldn't use undead for a few reasons. The command system might not be practical enough. For instance, a lot of warfare is strategy and even though this is early bronze age and you make us assume no other magic exist... In a world where this exists other magic would exist, we could therefor assume that most fights wouldn't even use regular soldiers to begin with since one spell could wipe a lot out if they weren't protected by some magic. So I'd assume that most battles would end up being some variation of the first world war with mages at distance throwing spells at eachother. Of course a lot of this depends on the societies work.

Another reason could be faith. Perhaps one faith believes that these undead are above other humans and thus shouldn't fight. Perhaps barbarians fight till then end and then rejoice as they get to fight again (think about how happy orks from warhammer 40k about fighting).

Society might hate these undead and think that they could only serve as miners or something like that.

In short you could use societal factors just as much as strategical factors to say that they wouldn't be very useful. However if you have a spell capable of making land mines... whispers to corpse run in that field

Answer 18

They use a mixture.

You'll have an officer corps. This may include undead, or even be dominated by it, with legendary generals brought back to lead people.

At the middle tier is almost all living humans. They vary from petty officers to NCO levels or privates.

At the bottom you are going to have undead conscripts. These have been whispered meta-commands to follow the orders of the middle tier living humans.

People are brought back from the dead in 4 modalities.

The top tier is your living god. Rulers who are killed in a pain-free way and brought back to rule as near immortal sovereigns. A given society could have more than one of these; they are brought back as a matter of status. These are the ones treated with expensive exotic substances to keep their body intact, possibly for centuries.

Next is the knowledge worker, the high end servant, whose death is too costly to waste. They are an expert in some subject. Possibly they are whispered words of self preservation and servitude while dead. These use a less sophisticated version of the living god model, and this is probably where the techniques used where practiced and perfected.

Under that are the citizen undead. When you die, you are brought back. Entropy is a bitch, so you decay over time, but it maybe gets you years or even decades. More expensive resurrection techniques in theory make you last longer, but maybe not. These are whispered words of loyalty and love to both the state/religion that brings them back, and to the people who pay for them to return, plus an inability to express the pain and suffering they are feeling (for marketing reasons).

Finally, the zombies. These are used as semi-disposable labor, and are whispered words that turn them into safe automatons. They use the cheapest kind of resurrection magic and preservation; they'll still be somewhat expensive, but they don't last all that long. People who cannot afford resurrection magic are recycled this way, including the already dead, as are dead slaves and convicts.

If we take this civilian use and give each undead sounding names, we have

Zombies: Automatons, basically slaves.

Ghouls: Undead citizens, brought back and paid for.

Reborn: Knowledge worker caste, often killed on purpose and brought back.

Neter: Ruler caste undead.

We can then map this back to the military. Zombies will be used, but they are disposable and stupid. Ghouls will be integrated with the common soldier, and exist in a squad or larger organization. Reborn would tend to be specialists or tacticians; your engineers who know how to build siege engines, for example. General class will be Neter.

Each of these jobs will be done with a mixture of undead and living, with the exception of zombies (who wants to arm a living slave?). If the living die, they are brought back. Foes who are killed are turned into Zombies and used in the next battle; zombies are the bulk of your losses, as they aren't very good at fighting (many are frankly suicidal, as their existence really sucks), but are better than nothing.

Note that the living troops learn how to fight, so when they die their undead ghouls still have the skills. A purely undead army runs into the problem that the "fresh" undead never learned how to fight, and using a slave caste to fight your battles is a good way for the slaves to take over the empire. Mixing undead with living, having the living in the command chain, reduces this problem.

As a bonus, the zombies can be used as pack mules. As they don't eat, they deal with the land-based "rocket" equation of transporting food for an army quite well.

Answer 19

There is a lack of bodies

Undead are good soldiers, but the problem is that it is not that easy to find good bodies to fight.

To start, the king would basically need people who died

• at a suitable age (and even in the antiquity, the death rate in the age of late teens-early thirties was still relatively low; the average lifetime of 30 years was so low because of child mortality, while the expected lifetime at 20 was more toward the 60 years)
• without a battle-impairing trauma (I think that some kinds of death, like drowning or because of fire, would impede somebody to fight effectively, if their effect can still be felt)
• not of plague/illness (the mages don't want to perform the enchantment on some potentially infective corpse)

This doesn't leave out too many options: an evil king could then decide to kill thousands of his subjects in order to have an undead army, but I don't think this would end well. He's basically creating an army of soldiers who would use whatever is left of their free will to hate him: if the "programming" during the enchantment is not all-encompassing, they would easily rebel and take revenge against the king.

The most logical option would be to fight with mortal soldiers, and resurrect the dead ones after every battle. This would mean that part of the gain of a victory would be some addictional soldiers from the enemy (provided it is possible to "program" them in a way that they couldn't rebel).
In this case, armies would still be mixed undead-human (with a growing percentage of undead as long as the campaign progresses), but I don't think there would be enough casualties to have more than half army composed by undead (probably a lot less).

This would also bring to another situation, where in order to avoid the risk to give more power to the opponent, the armies develop melee weapons that can kill a soldier in a way that doesn't allow to resurrect him (for instance destroying his head/body).

Answer 20

Depending on how the balance between biology and magic in your universe, the lack of ability to heal will be a major limiting factor in how long an undead soldier is usable.

If we assume that the undead soldier is powered by his own muscle movements (e.g. a zombie or mummy) as opposed to magic (e.g. your generic fantasy skeleton warrior), this will place a limit of the amount of activity they can perform without healing the micro-tears each action generates.

In order to contract their muscles, they need Adenosine triphosphate (ATP), which can be produced from either stored fat or what they eat. Assuming you don't want your undead to starve within months, I would imagine they use some form of magic in place of their finite fat reserves- so calorie expenditure isn't an issue.

If that is the case, then the limiting factor will be the wear and tear on their muscles. Armies are required to march considerable distances with their gear to where they are needed- while living beings can repair this damage, your undead will end a march permanently weaker than when they started. As they become weaker, marches get progressively harder to the point where they waste away at the legs.

This would lead to the undead not being very well suited to being standard foot infantry, and instead being required to be transported or garrisoned close to where they are reanimated- however, assuming they don't have to move much at their post they would undoubtedly be very useful as sentries and guards.

Answer 21

The undead are aggressively suicidal

They don't like being reanimated. At all. You describe them as feeling what killed them constantly which, combined with the likely scenario that the revival process itself is traumatic for them, will lead to them not wanting to live again, and seek any and every opportunity to return to the bliss of the afterlife (or the void of nonexistence).

They will follow your commands, but in such a way to maximize their chances of getting sufficiently damaged to nullify the revival spell. If you use them as an army for instance and tell them to attack the enemy, they will march, but then they will basically thrust themselves on the enemy swords.

This will make the undead to be largely useless without heavy supervision in any situation where getting hurt is even a remote possibility.

To not make them completely useless, you can have a small percentage of the undead that had a particular quirk of how they died an\or the way they thought before dying, who don't mind being resurrected and will be interested in avoiding being killed again. Adjust the percentage of those to suit your story needs.