War and battle is not about killing...

Summary / tl;dr

Yes, this military will be effective, because you will write that it is.

Your job as the author is to make it credible.

...it is about control

This is not even a platitude: war and battle is not at all about killing people, war is about establishing and/or keeping control. When you have control you have won the war.

And what is it that the belligerents want control over?

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  People, because people can do work and pay taxes; they produce value
  


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  Resources, such as mineral deposits, manufacturing, farmlands


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  Areas, strategic locations from which you can conduct operations, or use as transport routes

Now granted, it is "easy" to win control by simply removing someone that stands in your way, for instance by killing them. But killing is not at all necessary to win control. In lieu of outright killing your enemy, you need to either deny them the control they want, or make them unwilling to exert control over your people, resources and areas.

You said that this nation is by far the most advanced nation on the planet, to the point of having self-propelled armoured vehicles a full half-century before everyone else. This means they have two things with which any defensive force can win the war: mobility and communications.

1. Winning the information war means: always ahead of the invader

No matter what the invaders do, it appears that the defenders know — as if by magic — where the invaders are going to turn up next, and they always seems to be adequately prepared for this.

The "magic" in question is things like wired and wireless telegraphs, used by a vast network of observers, informants and agents. While the invader is on foreign soil, they have to rely on messengers to deliver physical messages, and all attempts at establishing instant messaging like a telegraph network is always thwarted by the defenders.

2. Nothing to control

Whenever the invaders show up at what they thought was a significant location, there is nothing there to control. The civilian population has been evacuated and relocated with astounding efficiency, the advanced machines that your nation is famous for have either been moved away or dismantled and hidden well, the invaders find mine shafts filled with water and no way to pump it out, the granary cashes remain empty or simply never found.

With few people in this defence force tasked with battle you get a lot of people available for preparations and transport. And even more people available to train and drill civilians in how to quickly and efficiently be relocated, out of the way from the invaders.

3. Disrupt logistics routes

"Amateurs talk about tactics, but professionals study logistics."

General Robert H. Barrow, Commandant of the Marine Corps, 1980

No invading military has ever been able to maintain control if cut off from their home-land. Your nation's defence has specialised troops that excel in messing up supply routes for the invading enemy, denying them food, resupplies, and — maybe worst of all — a way back home. That impressive iron bridge they invaders passed over yesterday? It is now a pile of mangled beams at the bottom of the ravine. That nice paved road through the marches? It got flushed away by an unnaturally appearing flood that soaked that whole area and made the roads completely impassable.

The invaders may get into the country with relative ease but once there the initial victory rush will be replaced by being bogged down in a logistical nightmare. This point and the one above would not be the first time in history this has happened.

4. Psychological warfare

— Hey, did you hear what happened to the captain's previous command?

— No, what?

— They disappeared... all of them. He went to sleep one evening in the camp... the next day... poof they had all vanished, like magic. Only he and his tent was left standing.

— You are pulling our legs...

— Try, ask him... see how he freaks out.

Sleeping gas and nets? Specialised in rounding people up and taking them captive? You nation's defence will be experts in cooking up all sorts of "mysterious" events that — when re-told by influence agents hidden in the invader's ranks — will demoralise the invaders really quickly, especially when cut off from home as mentioned above.

Add to that effective propaganda, outright bribes of entire military units, impressive — and frightening — displays of technological aptitude and skill, and you can soon have invaders that shivers at the kneecaps at the thought of trying to deal with this enemy.

One of the biggest demoralising elements of this is that the invaders are simply is not prepared for this. They have trained for traditional battle, of setting up face to face in the field and then clashing together. Nothing(!) prepared them for an opponent that behaves like this; they are not being out-battled, they are being out-manoeuvred.

The final blow is when the diplomats — with a confident smirk — convey the message: "And if you think this is bad, just imagine what happens when we decide to use force. I advise you to go back to from whence you came while you still can. Good day gentlemen, ma'ams".

5. The ultimate ace up the sleeve: author's say-so

In the end it does not come down to whether a non-lethal military would be effective in real life or not, but whether you as then author can make it credible; if you can make the reader willingly suspend their disbelief. This military — in your story — will be effective because you as the author will say that it is. The only issue is if you can get the reader to accept it.

No. In the words of General Georges Sada, "The purpose of a military is mostly to be strong enough that you never have to use it". A non lethal military fails in this test on several fronts.

1. When the other guy is shooting to kill, you lose people just trying to get close. He can choose to simply destroy your cover indiscriminately with one big bang from a distance, while you're constrained to get close enough to touch on every encounter. Your losses on every engagement will quickly wear your military to nothing while leaving the enemy at nearly fill strength




2. The majority of rounds fired in military operations are cover fire - they aren't intended to hit anything, their only role is to keep the enemy from shooting at you. If the cover fire is non lethal, the enemy will take more chances because a hit doesn't cost enough.




3. Non lethal (or more properly less lethal) weaponry can often be adjusted to. People who have been pepper sprayed more than once will often learn to continue through the irritation. Tasers aren't always effective. People differ in their reactions to anaesthetic gases.

Yes...

I second all of MichaelK's answer. Killing, while common, is not inherently necessary to win a war. I will add that historically it was far from uncommon for military units to surrender with minimal violence once they knew they were outmaneuvered. This was particularly common with mercenary units during the Renaissance but you see it all throughout history when you are dealing with professional soldiers rather than amateur militias. Logistics are also of vital importance in any campaign expected to last for more than a single battle.

A non-lethal military can be fully effective so long as it has other ways of achieving control.

But...

I'm writing separately rather than only upvoting MichaelK's answer because I think he is overlooking the difficulty of having believable, effective, non-lethal techniques using roughly Victorian era technology.

It is so difficult to create combat effective non-lethal weaponry that the term has fallen out of use in most military and law enforcement circles in favor of "less-lethal" weaponry.

Using any type of "knock-out" gas on a group is likely to kill at least some of them while risking leaving others at reasonably high levels of alertness and effectiveness. Getting the dose right on that is difficult which is part of why professional anesthesiologists exist. CS gas and tear gas have relatively few casualties, but they do not work well against an organized military force and are mostly used to disperse crowds.

Tasers are probably one of our better ways to incapacitate a resisting person non-lethally, but there have been instances of them causing death and other instances of them being almost ignored.

Nets work well against a single opponent, especially if you only need to incapacitate them briefly. They were famously used by gladiators in Rome who, despite some TV depictions, rarely wanted to kill their opponents. But incapacitating a unit with a net would be hard, especially if you need them to stay that way for a while instead of being able to extricate themselves.

Other less lethal technologies such as active denial systems based on sound or microwaves are likely out of reach of Victorian Era technology and again are more about crowd control than facing an organized military.

If you are writing a story and want verisimilitude, the hard part will be selling technology that is both effective and non-lethal. This changes of course if you add magic or science-fiction style hyper-tech which would allow you to almost hand-wave this problem away, but if you stick to Victorian era technology it may present challenge in keeping it believable.

Of course it could. There are many ways that they could still be a force to be reckoned with. There is a historical precedent for most of it.

The main role of the military is a deterrent

The military does not exist solely for invasion and conquest. It’s main role is for bargaining and actually using it is a last resort. If an international dispute can be settled by diplomatic means or economic agreements, then that is still preferable for both parties than a confrontation. Even during the Victorian era, diplomats played an important role and there was a lot of communication between leaders to attempt to avert conflicts.

A non-lethal military operation could still be disastrous for a country with territory seized, soldiers captured, and commoners turned against their own government. Especially if this Empire is vastly more advanced than neighbouring countries, then a conflict with it would still be detrimental as would rebellion within.

People don’t fear death that much

Lethal force isn’t that effective as a deterrent. A military intimidates another nation and its government but doesn’t stop individuals stepping up to confront it, eve in the face of insurmountable odds. In the face of ideological differences, the fear of death can be overcome. Many people still stand up to tyrannical regimes even if they use lethal force, torture, or other human rights violations. For some, Martyrdom is even desirable or glorious.

People still commit crimes in the face of the death penalty. Countries that use the death penalty don’t have lower crimes rates than those that have abolished it. Death is an abstract concept that we haven’t experienced so it doesn’t function that well as a deterrent. We all think, it won’t happen to me. Close calls are known to result in courage among the survivors. This was evident among the survivors of the London Blitz, it strengthened their resolve to continue to support the war effort. It was not effective to break the morale of the everyday people.

Dropping bombs on a country doesn’t typically convince the local people that you are there to liberate them. We’ve seen more technologically advanced militaries fail from Afghanistan to Vietnam because they didn’t understand the importance of how they were perceived by the local people. An military employing lethal force is not necessarily effective and some cases the resistance to them only grows as more people turn against them. In this respect, an Empire using non-lethal force could potentially be more effective as they can resolve isolated conflicts without being condemned internationally or turning others against them.

Non-lethal weapons still cause harm

A regime employing only non-lethal force is still something to be feared. Many chemical weapons are considered war crimes against the Geneva conventions, even if they are not lethal. It is still possible for this Empire to be authoritarian and incite fear among their own people or other countries. They would not necessarily be harmless simply because they refuse to kill.

They can still maim and injure people on the battlefields. They can still capture, imprison, torture, and enslave people. They can still use poison and destroy property. They can still push a region to the brink of starvation and economic collapse by burning their crops and destroying their infrastructure. They can still deploy chemical and biological weapons to cause mayhem and suffering at a massive scale.

The decision to have an Empire which does. It use lethal force does not limit the scope what else they can be. Just as countries with nuclear weapons and torture camps can settle disputes diplomatically, likewise an Empire without these can still choose conquest and the violations of basic human rights. These are not mutually exclusive.

Perhaps the most interesting consequence however will be the vast number of survivors after any conflict to tell the story. Anti-war sentiment grew in conflicts that draw media coverage and showed the experiences of the front lines. From the poets of WWI to the filmed broadcasts of Vietnam. If there were more survivors to share their experiences, this would greatly affect public perception and the world as a whole (in way that was otherwise not possible without modern communication technology).

No, it would not and could not be effective

Social issues: Larry Niven's 9th law states "Ethics changes with technology". Applied to this situation - through most of recorded history, human life has been little valued. When infant mortality rates are so high that couples expect to lose one or more children before they reach adolescence before injuries and disease reap an early harvest amongst the older demographics - death may not be desirable, but it is considered normal. Capital punishment has been routinely practiced by almost all societies, sometimes for trivial offences such as petty theft. It is only in the last few hundred years that increasing technology has led to the economic prosperity has made it financially possible to deal with common criminals through imprisonment rather than execution.

In short - despite the beliefs of some humanists and/or religious teachings, there would be no social will to outfit a military with non-lethal options routinely. Even riots by a country's own citizens were routinely dealt with through the use of bayonet charges and/or the use of live rounds - see the history of the Riot Act. It would be inconceivable to treat enemy combatants with kid gloves.

As noted in other answers, the other social issue with a non-lethal military is that it lacks deterrent effect. If the worst that will happen to your enemies is that if things go badly then they go to sleep for a while - the opportunity to get some extra sleep is generally considered a bonus to most soldiers.

Technological limits: "Sleeping gas" - the use of various gases as a means of general anaesthesia during surgical procedures gradually became more effective throughout the 19th century - effective meaning that the patient was anaesthetised but did not die. The reduction in lethality was due to improved methods of controlling the dosage when the gas was applied using a mask held over the face. There were certainly no gases known that could be deployed over a wide area of the battlefield that would a) reliably put humans to sleep; and b) not kill lots of them.

Regarding defensive measures (to allow the use of relatively short-ranged non-lethal options) - armoured vehicles have significant limitations even today. Early armoured vehicles were extremely slow, unreliable and short-ranged. For personal protection, the type of armour available in the late Victorian era was basically steel plates, an example being that worn by Ned Kelly. (It didn't work out so well for him.) Such armour could not be worn continuously and provides limited protection against military firearms of that and earlier eras.

The other issue to consider is that warfare encompasses many settings. In a naval battle it would be almost impossible to effectively use any non-lethal measures against another vessel without precision delivery of munitions that only became moderately affordable in the late twentieth century.

The best option for a truly defensive-minded military with a monopoly on late Victorian era technology (assume all other countries are 50+ years behind) is to have a conventional (lethal options) military which can react quickly and overwhelmingly. The empire can achieve this through:

• a monopoly on near-instantaneous communications - no one else has telephone networks and few have telegraph


• strategic ability to rapidly deploy military forces - vastly superior train networks and motorised troop transport naval vessels


• overwhelming naval superiority - no one else has naval vessels that are ironclad and motorised equipped with vastly more powerful and long-ranged guns.

Simply being too scary to even consider attacking is a much better way to save lives than getting into lots of fights and relying on dodgy, (possibly) non-lethal options that are beyond the technological limits of the era.

Yes, but somehow it must be effective.

Effectively, it would be more like a "world police".

How exactly, it depends. Some example:

• They might far outnumber any possible enemy military by mass.


• They might overwhelm them technologically (for example, bulletproof shields and vests).


• They might have a strong, world-wide security service system, gathering data and solving challenges before they could emerge to a visible level.


• Or all of these, combined.

So, your military does not kill. How very nice of you! But how would you win a battle? You calculate on non-lethal methods to impair the enemy combatants. Congratulations! You just knocked out a few thousand enemy soldiers... But what now? Will you let them go? That would be backbreakingly stupid, they could return to fight again. So you have to imprison them.

Fastforward to after you won a few battles: You have a massive amount of prisoners of war, who must be guarded, feeded and housed. These prisoners will drain your ressources, and the danger for prison escapes or revolts is high. Sooner or later, even if your military is succesfull in the field, you will run into massive problems regarding logistics.

As cruel as it is, prisoners of war are mostly a small number of the enemy combatants, because most of the enemy soldiers died or fled. The only occurences of large numbers of POWs was when enemy forces were surrounded and surrendered.

Result: Even if (and that is a big IF as others have pointed out) your non-lethal military wins a few battles, the number of POWs will crush your logistics.

Yes, but it's complicated - that's why no one has ever tried to do it in reality.

An army can be used on the offensive or on the defensive. If the latter, its more important quality would be the deterrence factor, so is, the ability to make other countries not daring to attack you. On the offensive the most important thing is the ability to take control of enemy territory - and negate the efforts of the enemy to regain it. Neither quality requires killing people, but it's harder to do it without killing.

Actually, a non-lethal army has many advantages over an homicidal one, which is its ability to win the hearts and minds of the vanquished. When USA toppled down Saddam Hussein's regime in Iraq it might have expected some kind of gratitude and a positive feeling about them in the country. Well, no. If you could conquer a country without killing its people - say, releasing the enemy combatants after some time as prisoners - you would find the task of ruling the recently conquered area much more easier. Govern them a little better than they were before and mostly respect the local culture, religion and language and pretty much you have incorporated a new batch of happy citizens to your empire.

The deterrence factor should not be a problem, then. If country A attacks your empire, you defeat them and incorporate part (or the whole) of the attacking country into your empire. Nobody will dare to attack you anymore.

The problems with a nonlethal army are not strategic, then - you have the upper hand there - but tactical. In actual battles, non-lethal weapons are in clear disavantage against lethal ones. They are usually short-range, are not guaranteed to stop your enemy and aren't scary, so it's unlikely the enemy is going to surrender or flee without fighting.

A nonlethal army, to be succesful, would need being (nearly) invulnerable to enemy fire. If you don't kill them, but they can't kill you then your army does not have to fight against the burden of losing lives without inflicting casualties. A certain sense of superiority morals can make your people to sustain some casualties without resorting to revenge, but if your casualties are too high (being too high a really low number) the morale will crumble. Also, the fact that the enemy can't kill your people will make clear to them that the resistence is futile and they are going to be captured if they continue the fight, so they are going to be more inclined to surrender or desert.

If they are not really inmortal, at the very least they'd need highly effective nonlethal weapons. If your troops have stunning rifles able to disable an enemy a kilometer away, with 95% success rate or higher, they at least can try to play it safe; keeping the distance, trying to fight outside the effective range of the enemy and not exposing too much. Your weapons must be able to incapacitate the enemies more or less permanently, however, since you can't approach your targets until they are all down. If your weapons can do that, this is in fact an advantage over lethal weapons. In modern warfare usually maiming is preferred to killing, since when you injure an enemy you usually take out three enemies per shoot: your target and two comrades who are going to take him to a hospital.

All of these restrictions put you in a scenario where your empire must have an overwhelming technological advantage over your enemies, to the point they can be considered gods. Think about spanish conquistadors in America: they didn't have nonlethal weapons but had they used them the result would have been pretty much the same. Since their armors and horses made them nearly impossible to kill, the natives despaired and surrender, even with massive numerical advantage. The spaniards killed the enemy combatants, but being captured and slaved was equally threathening, so nonlethal options, had they been possible, would have worked pretty much the same.

It can work, but only with some meaningful edge

The military is not a killing machine, believe it or not. The military's purpose is not to kill the other guy. The military's job is to accomplish an objective important enough that they are permitted to leave the realm of civilized life in order to achieve it. To describe them properly requires a double negative of sorts. It's not that they will kill to accomplish a goal; it's that they are not bound to not kill while accomplishing a goal.

If you look at modern American combat, they do indeed operate with tremendous bounds. The rules of engagement can be tremendously frustrating for a soldier. Limitations on how one is permitted to return fire when an RPG firing enemy hides behind women and children can test the patience of any soldier. But if anything, it does show that a military can operate in heavily restricted rules of engagement. Non-lethal is merely one such heavy restriction.

They accept these limitations because we can indeed accomplish the objectives within them. It may cost more (and we do hate how much the military costs), but we can accomplish it.

However, put the military in a more symmetric situation where such rules of engagement may prevent our ultimate objective from being accomplished, and those rules of engagement will bend or break. Rules may become more conditional, requiring non-lethal force up to a point, and at that point one finds out the full lethal potential of a military superpower.

The President of the United States still holds the launch codes to 4,018 nuclear weapons (2017 number from treaties we have signed). For the most part, we operate under the rule that these weapons are not used. It is a level of lethality that our rules of engagement simply do not permit. However, the fact that said launch codes still remain valid points to where the military can go in the name of accomplishing an objective.

So the real question to ask is what will your non-lethal military do if non-lethal force is insufficient. Do they actually hold themselves to non-lethality, even when faced with the risk of complete eradication of their society? Or is it more of a preference, with the lethality built up behind them.

Most people's understanding of the military is much more of the latter. I don't know of any service men who are in the military for the purposes of killing people (though they may exist). The service men and women I talk to all recognize the need to be prepared for the moment when a need to achieve an objective in the name of right outweighs our normal rules of civility. They, of course, have varying definitions of what "right" is, but their opinions tend to follow that common structure.

We see this also in warrior monks. These warriors are some of the most peaceful people you will ever meet, but they train for combat incessantly. How one trains for combat in a peaceful realm is indeed one of the great challenges the monks seek to solve.

For a fictional example, consider the Octospiders from Rendezvous with Rama by Arthur C. Clarke. The Octospiders are a completely peaceful species, but 100% of their species is their military. They will seek non-lethal solutions to absolutely everything. They do this because they understand the consequences of failing to find such a solution. Those consequences are built into their genetic code.

Faced with a threat so indomitable that no peaceful solution can be found, the Regent Queen of the Octospiders can call for a vote to go to war. Calling for such a vote signs her death warrant. If the Senate votes not to go to war, she is put to death. Such violent desires cannot be permitted in a Regent Queen once detected. If the Senate votes to go to war, the many (or even most) individuals undergoe a genetic level transformation. They become warriors. These warriors do not stop at anything. Their ultimate goal is never anything short of xenocide of the entire species which is threatening them. At the end of this quest, the queen and all of the warriors are put to death. Once again, this level of violence cannot be permitted in the Octospider world.

The Octospiders are not truly committed to non-lethality, but they are an excellent example of how a species may operate up to a point, at which point a switch is flipped, the rules shift, and something happens.

A nonlethal military defending against a normal military is in the same position as a modern nation defending against stateless terrorists, in one sense: that "we" have to get it right every time and "they" have to beat us only once to do harm. The normal/lethal military can try, try again, because there are no permanent consequences to a failed attack. So your nonlethal military has to have an incredible technology and training advantage (think 8-foot-tall bulletproof fighting robots) in order to just hold its own. And even then, the enemy could win a war of attrition by using surprise attacks, booby traps, and the like. Every non-lethal supersoldier they kill is one you can't bring back.

What's more, when you're talking about an incredibly powerful, high tech, superpolice force with fighting robots or stormtroopers marching around and gassing or tasering people... that's exactly the sort of force that people are likely to rebel against.

On the offensive, it's even worse. To capture territory, you'd have to knock the enemy out with gas or something and then physically move his unconscious soldiers back to the new front line you want to establish, before they wake up. That would be incredibly hard labor and risky.

The military would only have a limited deterrence value.

The empire demands something from another country. The right to establish a coaling station, the right to sell opium, or an apology for the mis-treatment of a citizen of the empire. The other government considers their options. They can give in, or they can fight and then give in if the fight goes against them, or they can fight to the bitter end. Their choice will be influenced by the balance of power and also by domestic politics -- if the leader gives in to foreign demands, how long will he or she stay a leader?

If the empire employs non-lethal weapons, then an initial round of fighting to establish an favorable negotiating position sounds like a good idea. Soon the empire will be swamped in countless little wars.

An old saying goes:

One can fix anything but death

If we apply it to this case, we realize the following.

For sleeping gas an antidote or an appropriate mask can be developed, for nets a proper way to cut them can be invented, shields can be broken by an appropriate amount of energy. For a skull (and the brain within) smashed by a bullet nothing can be done.

A wounded enemy can still fight back, or, even worse, if convinced of his death can even become more aggressive.

So, no, a non lethal force is not sufficient against a motivated enough enemy. A dead enemy is way more safe to deal with.

No, a non-lethal army would not be effective in protecting the country.

Once countries that field lethal armies figure out that all they have to face is guys with sleeping gas and nets, they'll tear the non-lethal country apart. A million men with rifles, maxim guns and artillery would utterly crush an army with sleep gas (if the wind is blowing in the right direction), shields (which are not bulletproof with late Victorian tech) and nets (issue soldiers a bayonet).

Lethal army troops could slaughter the non-lethal soldiers with maxim guns or with 1865 gatling guns. Lethal soldiers could mob armored vehicles with molotov cocktails and similar weapons. Even an army of Mongolian horse archers could slaughter the non-lethal army. What do the lethal soldiers have to fear?

Even if the non-lethal country is the most advanced country, look how the Zulus fought the British despite massive losses. Against a non-lethal army, a lethal army has nothing to lose.

Technically: Yes, absolutely.

It actually hurts the enemy more if you leave their soldiers alive but crippled. So use biological weapons like illnesses (catapult infected corpses into enemy camps or cities, set animals free closeby that carry diseases, etc.), poisoned weapons (dip your cutting implements in a rotting corpse or feces before using them), chemical weapons that cause blindness, sound bombs that cause deafness, splinter bombs and mines, expanding low penetration bullets, etc.

Now if what you wanted was a way to keep the moral high ground, then I think that's possible too. But all the other answers already go in that direction.

It Depends on the Mission

Canada and China come to mind as countries that, while they both have very lethal militaries, mostly send them on missions where killing is not part of the plan. Canada doesn’t defend its land border, and would be worse off if it tried. It sends its forces mostly on peacekeeping missions where winning means winning hearts and minds. China does use its armed forces to deter and even threaten its neighbors (although, in a farce, even this could be an elaborate ruse), and I don't want to gloss over how it treats its own people, but as for actual military operations, it sends its troops on a lot of rescue missions and to respond to disasters.

El Salvador is the modern example of e country with no military at all (largely owing to the historical role of the armies in the region in domestic politics) and the colony of Pennsylvania was a historical example of a polity that was pacifistic for religious reasons, and therefore needed to maintain good relations with its Natives rather than try to intimidate or eliminate them. (The British Army, however, was also around to back them up.)

So, there is some historical basis for a country that plans to only use its military for the equivalent of law-enforcement and emergency-response missions. Maybe it gets along well enough with its neighbors and is so much smaller that trying to fight them would be counterproductive. They're better off being ostentatiously kind and harmless.

Would non-lethal mean non-wounging?

A number of modern landmines (like 72b frog mines or bouncing mines) are designed to wound or cripple, more than to kill. A wounded soldier needs to be protected, transported to safety, and healed. It mobilizes resources, other soliders, and is often more profitable than just killing them.

If you kill a soldier, others will keep fighting, if you cripple him, 2 or 3 will have to stop fighting.

However I'm not sure if this technique can be used for all of warfare instead of just as a "side bonus".

Would a non-lethal military be effective at protecting a country [from lethal a lethal military]? Barring technology that makes them entirely impervious to death, the morale of that military is going to dive considerably the moment they start taking losses and have nothing to effectively counteract. Worse yet is that the forces would have a hard time protecting themselves, protecting the country becomes even more difficult.

Making non-lethal tactics available as part of a larger arsenal is not bad, and there is a growing desire to shift that way with technologies being developed in the Less Than Lethal field to assist military forces in quelling populations that may largely be civilian.

Also know, that military forces adapt to the tactics of their enemies, and develop technologies to counteract strategies they encounter. Sleeping gas might be effective a few times but then the next wave comes with gas masks, shields may be effective initially but then they develop larger, more powerful weapons, and so on.

So, I would posit that an entirely non-lethal military might be at least initially effective, as a long term solution it will be very difficult to maintain. Again, barring some sort of technology making them entirely immune to taking casualties.

A chapter out of Roman history would indicate it is more effective to utilize psychological warfare, for example if you were to march into an enemy zone with ten thousand soldiers. You would then also have to account for the upkeep, whereas it would be easier to masquerade an army size of ten thousand when really you have less then half that. Giving enough reason for scare tactics and utilizing the control zone to your advantage could prove just as threatening as any real show of force.

Judging from the history of this planet, there are two avenues to peace:

1. Peace through communication;


2. Peace through superior fire power.

Communication does not appear to be winning the hearts and minds of a strong set of Humans but it is by far, the superior mechanism to win a conflict.

If you were cast away to a primitive planet, filled with stone age people, and you only had one handgun with 9 rounds of ammunition would you be able to take over and create an empire on this planet?

After you ran out of bullets you would be left with your superior knowledge. You may obtain a foothold on establishing your new empire but you would be on an equal footing with the inhabitants after the bullets ran out. What gives you your advantage is not the ability to kill everyone but the ability to kill a single person.

All you have to do is get control over a few individuals and you can exponentially build your power base to control the whole planet.

Having control over those warriors who would willingly offer their lives offers you superiority over any military force. The mind is always the best weapon. Superior communications coupled with loyal followers can win against a physical military force.

In the end it is a people's fear of death/pain that determines who will win any mortal conflict. If you control the mind you control the body.

Many good answers already. Let's get a real world example:

In the Annexation of Crimea by the Russian Federation, little green men took control of Crimea. This annexation was almost entirely bloodless. According to Wikipedia, only 2 Ukrainian navy personnel died (and 15,000 defected). Looking at the context, this death looks more like homicide than military combat:

The defence ministry spokesman said the soldier had been preparing his belongings to leave for the Ukrainian region of Mykolaev on Wednesday when an argument broke out with Russian servicemen.

It certainly didn't appear as necessary, due to a combination of (in order of importance):

• Support among the local population


• Element of surprise (what the heck is going on?)


• The (implicit) threat of violence: although they didn't shoot much, they certainly were armed

Apparently, the nature and conditions of the Russian operation were such that the Russia was able to take control of Crimea almost entirely without spilling blood.

Depending on your world's culture and politics, it could range from totally useless to absurdly effective.

As a general rule, human beings do not like killing other human beings. This is as far as we know, a universal instinct found in all human beings except maybe in people with certain psychological disorders.

Obviously, this instinct can be overcome. But how? There's a few ways it's been done:

1. You could dehumanize your opponents. You can't feel bad about killing another human being if you don't think of them as human beings anymore, they're now just untermensch. Obviously, this was and is the primary tactic of most ethno-nationalist and racist ideologies.




2. The above is typically paired with self-elevation. If your nation or ethnic group comes to think of itself as superior to all other races, a race of übermensch, then the killing of others becomes acceptable.




3. Alternatively, you could exploit ideological or cultural fervor. Convince a group of a 'greater cause' worth killing others for. This is the primary tactic of religious militarism and ideological crusades. (Heretics, bourgeoisie pigs, communist scum...) This is virtually always paired with a cultural elevation of war and militarism itself.




4. A variant of the above is to exploit personal, national, or ethnic self-preservation. People will take up arms if their way of life -- or life, period -- is on the line. This is generally accepted as justified but can frequently bleed into the above (the Cold War was frequently justified by this tactic by the United States and Soviet Union).




5. Another variant is to simply appeal to revenge. Maybe they've conquered your homeland, maybe they've bombed your family, maybe they burned down your farm, maybe you think that you wouldn't be poor if it wasn't for them. This can be a powerful appeal to take up arms, and is the primary technique of many extremist ideologies.




6. But maybe you don't need to justify it, but instead distance yourself from the idea. In this case, soldiers and warriors could be relegated into their own disdained class, possibly even considered an under-caste. In this way, the ruling class can take advantage of war, while simultaneously disassociating themselves from the concept. This requires a strong social or ideological hierarchy to pull off, otherwise you couldn't force people to war for you.




7. Finally, you could appeal to necessity. Simply avoid killing people as much as possible, but justify what suffering occurs as 'unavoidable' or 'the reality of war'. This is the primary tactic favored by modern democracies and is reflected in the way their militaries fight. (But conversely, and rightly so, a large portion of people are skeptical as to how unavoidable or necessary it really is.)

All this is to say -- which ones of the above are predominant in your world? The answer to that question is the answer to how effective a non-lethal military would be.

If the systems at the top of the list are the primary ones of your world? Then it would be almost totally ineffective. Nationalist and racist ideologies necessarily depend on the glorification of war and death, so pacifist tactics would simply be looked down upon.

What if your nation adopts pacifist warfare, but it's still oppressive or colonial in some way or the other? Then the reformist and counter-movements would necessarily tend towards more militaristic beliefs. The bigger of a deal your empire makes of its pacifism and the more brutal or oppressive it is, the more likely this is.

Finally, if your world is (attempting to be) primarily democratic or egalitarian? If your nation is genuinely democratic and pacifistic? Does your pacifist technique or technology actually work? Then it would be stupidly effective. Modern dictatorships and ideologies attempt to portray themselves as democratic ("People's Republic", sham elections, populism...), and to portray the opposition as being 'worse' or 'just as bad'.

Being able to fight wars without killing would be an ideological coup. Modern anti-democratic ideologies appeal to the senses of self-preservation and revenge to recruit new members, while racist and militaristic ideologies attempt to portray themselves as equal to the others. They would continue on through inertia, but they would be greatly stymied.

Dictatorships would be in greater trouble, as they rely on the threat of death to eliminate opposition leaders and to prevent people from joining them. This would be far more difficult in this world. A dictatorship would either have to rely on imprisonments and assassinations to keep people in line -- something which is hard to keep secret, even at the best of times. Or they would have to fully pivot and embrace militarism and murder, abandoning any pretense to being a democratic nation.

A dictatorship could deal with it by appealing to nationalism or ideology -- but ideologies don't last forever. And obviously, the other democracies (and semi-democracies) of your world would have to join you to maintain their own consistency. (Though maybe a particularly militaristic democracy would avoid it, if such a thing could exist.)

The end result would be a world where death is no longer an acceptable part of war. War, if you could even still call it that, would presumably involve capturing the opponent and engaging in prisoner exchange. Combat would simply become an extension of diplomacy. As the 'first mover', your nation would gain a tremendous advantage, though it would eventually be equalized once the others catch up. And if your nation was the inventor of the concept, it could continue to claim credit for it, perhaps indefinitely.

Obviously, this is just scratching the surface. How things play out and how things end up depends greatly on the cultures in your world and something else totally different could happen. There's a lot of possibilities, and you'll simply have to think it through.

How about a highly efficient network of super spies that are able to infiltrate, capture and bring to trial any 'war criminal' who should attempt to start a war.

Effectively decaptitating any possible enemy prevents attack.

Note this mechanism could complement other suggested approaches.

If your army is big and technologically advanced to be able to most attacks from technologically more inferior enemy (or quickly recapture any that get through, with optional retaliation - like capturing all adult males, or all children), and you don't care about conquering other countries (just defending yours against them), then yes, it will be effective.

As other metioned, the big issue is what to do with prisoners:

• 
  Returning them to their homes is bad, as they will attack again tomorrow knowing nothing bad can happen to them.


• Putting them in prison camps will act as an effective deterrent, but will eventually wear down your own population which will have to guard them (or risk rebellion)


• you can never trust that they will remain loyal if you try to integrate them.

There are however quite a few non-lethal deterrent options, which will reduce any further attempts to attack you. For example:

• If you technological level is way higher than anybody else and you can keep it that way (like, you're controlling all ore-rich areas), you can transport most POW to that far away continent (or similar hard-to-reach area) where they can survive (but not escape from), and which no other nation can reach (as their wooden ships with sails are way too fragile for that violent high seas which only your metal battleships can pass), while letting a few POW back home to spread a story. So families will certainly lose their breadwinners for life if they go to attack you, and will know that. Hence, they're more likely to revolt against their own government if forced to do so, rather then to attack you.




• alternatively (and more dystopian), you can terrorize or brainwash them and then return all of them to their homes, where they will spread your propaganda (or even revolt against their own countrymen) until their own government has to put them in prison or kill them. Or they can be so psychologically broken so their government will have to spend year and a lots of resources on their rehabilitation before they can become productive members of society again.




• Additionally, you can use drugs (which only you have advanced knowledge and machinery to produce) and make some small number of them addicts, let them experience the withdrawals, and promise them regular doses as long they keep providing you with useful information about their government, and then release them to their homes mixed with their own undamaged soldiers.




• you could also make it known (and followup on that) that for any attack, you will raid their cities with overwhelming advantage, steal all their infants (all those young enough not to remember), and raise them to be your armyman. And/or use they as live shield against their attacking armies until they grow old enough, so they'll firstly have to kill their own children each time they attack you. If they do not attack, their children will grow and live good and prosper, but will now know of their parents as they will become your own people. Or even, you can advertise such kidnappings as humanitarian action for bringing prosperty and good life for poor starving children who lost their breadbringers because of misguided violent attacks of their fathers, and you are teaching them how to overcome such barbarianism of spilling blood in event of war.

Attacking a country infrastructure e.g. communications and services, or their banking system, (which is basically what happened in 9/11) if you have superior, or more ruthless forces, it's obviously easier.

I believe one of the Nazis tactics during WW2 was to kidnap children from the countries they invaded, those with arian traits, basically. Russia has traditionally used scorched earth tactics and it has worked for them because Russia is huge, it worked against Napoleon's and Hitler's armies, obviously the weather helped as well.

In the modern world not only does USA have a huge army but they are technologically advanced,to such an extent that they are almost untouchable.

Yes, a non lethal army can be effective, but it requires the enemy to diligently attempt to save their own people. If you have a 100% lethal laser gun that vaporizes the target, the enemy no longer needs medical supplies, medics, stretchers, grave diggers, etc. If you spray the opponent with little bits of metal that will cause bleeding out in the next 10 minutes, they need two guys to carry off the wounded (two unarmed targets to shoot at), supplies (some of which need electricity), a medic tent, doctors, chaplains, shovels, etc.

You can make things much harder for your opponent by not killing them, not to mention the impact on morale when you are spared by your opponents repeatedly.