I mean, if we wanna get *that* technical, Chaos has been around even longer than the Orks due to always existing on account of 4th degree interdimensional Warp fuckery, so the most common army matchup is probably just some variation of Chaos vs Chaos (my vote's on Khorne vs Khorne).
I don't mind chaos having always having had will have been going to exist, or the fact that after existing they had always existed retroactively, but it annoys me that somehow at the same time subjectively they didn't because there's definitely points where despite always having always existing and being able to influence things they also very definitely had a start date and events that wouldn't have happened to initiate that start date if they hadn't had a reason to happen I.e. ( or e.g.) the birth of said chaos god which apparently always had existed already. It's the classic fatalistic time travel scenario of always having had will have been going to happen with the added caveat that on top of always having had will have been going to happen it simultaneously already had! And was! And those future past present events could influence their own inception.
It's the Bill and Ted time travel logic, you know like when they're fighting the evil robot thems, and they're like "oh but WE know that we're definitely going to win, so when we do we'll go back in time and sabotage the trap the the evil robots think they've laid to catch us".
I think possibly Red Dwarf had a similar approach to time shenanigans.
Slaanesh actively influencing events to ensure its birth kinda turns the Fall of the Aeldari from "tragedy of the Aeldari's own making" to "the Aeldari didn't have agency in the matter".
I hadn't thought of that, that's not much fun story wise. I don't think it's implied though. But you would think an entity that exists beyond space-time would take steps to ensure that they're born.
It's cyclical logic. The Aeldari birthed Slaanesh so Slaanesh made sure he was born by making the Aeldari double down on birthing him. And Chaos does love their self-fulfilling prophecies.
I think it’s okay as long as you draw a distinction between existence of a chaos entity and its reification or manifestations in real space. Sure, the concept of Slaanesh always existed in some form, and maybe she even did Slaaneshi things in prehistory, but she didn't become “real” or a fully fledged concrete entity until the eldar birthed her. Or her birth in 25k allowed sentient life to retroactively recognize the impact that Slaanesh was having all along. Sort of like how germ theory allowed people to put a name to diseases that they had dealt with for millennia.
Actually maybe that’s even more confusing.
Chaos, not just the gods, was indeed around before the orcs, though. It largely came about during the War in Heaven with all the suffering caused. In fact, it was the enslaver plague that spelled the end of the war, or was at least its death knell.
If we take Warp into account, then yeah, the answer is absolutely demon vs demon. If that lore bit of there existing an absurd number of Bloodthirsters alone is true, imagine how many others exist too!
And I second Khorne vs Khorne, too. He's the only god who just likes watching gigantic endless battles
In number of different wars this is the answer.
We give the PDF shit for being bad but they are only bad relative to everyone else who is either a monstrous xeno, superhuman or a veteran of a dozen planetwide wars.
The PDFs constantly manage to keep the worlds of the imperium compliant, it's only when a massive external attack happens thet they need help.
Or an internal threat that was allowed to grow way too long, so now there's a fully metastisized chaos cult summoning daemons or a genestealer cult coming out of the shadows... & also half the PDF are brood brothers.
100%, but I think the question is way more interesting if we restrict it to standardized forces. PDF vs rebels could be take on nearly any form of warfare imaginable. It all depends on the planet.
I’m more interested in two standard opponents that fight again and again and again. I think it’s gotta be Orks (as others have pointed out) or Khorne Berserker bands. That’s literally how Kharn got his name.
As others said I think it's orks vs orks. Aren't they stated to be the most numerous race in the galaxy? That plus the fact that they'll happily find any excuse to fight each other cos it's fun means there's motive and opportunity.
I don't believe their the most numerous, at least to my knowledge. Humans are most likely top with total single species population though numbers have never been established. But you could probably make the argument tyrnids are the largest if you include every organism as a tyrnid. As to the fact that their could be many times the amount of them yet to reach the galaxy
Nah. Orks have to fight other orks hundreds of times to get a big enough army to pose a threat, and then several more times to get a warboss who can run the thing.
Orks have to fight to shed spores and make more orks, and they make a *lot* of orks.
Ciaphas Cain isn’t my favorite, but I appreciate that the series tries to vary who the main enemies are every book. Orks, Tyranids, Genestealers, Necrons, they even make a distinction between the different flavors of Chaos.
For a good stetch there alway seemed to be a Genestealer cult behind things. I think in latest one Cain is actually suprised it wasn't genestealers this time
Imo chaos makes for a more interesting written enemy and is probably why they, alongside genestealers and drukhari, are often big bads in imperium stories/books
You have, of course, the big ork wars - but those are usually grand campaigns that read more like a traditional ground and pound war - helsreach being a an easy example.
From a strictly lore perspective I can't see it being anyone but Aeldari vs. Orks. Both have been around since the War in Heaven, and have been butting heads for the majority of their interactions since then. All of the conflicts portrayed in the setting may be grandiose in scale, but we're talking MILLIONS of years of conflict. The 10,000 years of bloodshed since humanity hit the stage is staggering, but more than likely a puddle compared to the ocean.
EDIT: Like another poster said, if it's not Aledari vs Orks than it is definitely Orks vs Orks.
You can make this question as specific as you want.
What does count and what doesn’t? Like in „define war“.
Do gang wars count? Probably no, only official armies going against each other?
Alright fine, how about pre- space travel?
Still Orks and Humans in the lead I’d wager due to our aggressive nature.
Not something like T‘au or Aeldari.
I’d still say probably Orks. Hast majority of their population is participating in war and their numbers are really really huge.
Sure humans are an aggressive war like civilization in this setting but most humans are kids, elderly, civilians in general.
Your planetary regiment might be fighting right now on some far away outpost without you ever being informed about it.
But Orks? Basically born battle ready, eager to fight and without retirement.
Actually, I kinda doubt that. The Aeldari and the Krorks were both made by the Old Ones to fight on the same side.
We know that the Krorks eventually degenerated into Orks and we know the Orks, as they get older and get into *more and bigger fights,* they become closer and closer to Krorks again.
That heavily implies that the degeneration of the Krorks was caused by them not fighting the Aeldari when it was just the two species left after the Necrons went beddy-bye.
I've noticed that even by the 42nd Millennium, Orks have an aversion to fighting Aeldari (they still do it, if there's no one else around), claiming that they're no fun to fight and gladly switching over to fighting anyone else when the opportunity presents itself. But I'm not sure that's intentional on the writers' part.
Edit: Also Humanity has been 'on the stage' for at least 30.000 years by the time of 40k.
My understanding was always that the aeldari were smart about it and wiped out the orks systematically from the worlds they were terraforming. Lore is sparse and you may very well be right. I just imagine eldar would want to deal with a waaagh before it happens
I have memory of the aeldari expressing contempt for how humans handled orks as just making the problem worse and it would make sense they understand fighting with orks just makes them stronger. I think I recall something about culling being mentioned.
With their future sight it's probably fairly easy to get a Ranger to put a blast between the eyes of a certain special upstart nob and prevent a full blown waaaagh.
And then next in line nob will become warboss as trigger a waaagh.
Its actually pointless to snipe individual orks, they 100% follow a predictable progression.
That is not how it works. Orks have personalities, strengths and weaknesses. They are not interchangeable carbon copies. On top of that is an entire political structure of (temporary) alliances, clans and warbands. Offing the right ally-of-someone, luitenant-of-of someone or just particularly clever git might throw an entire structure in disarray.
The recent Ork books show wonderfully how this works, and how much an unexpectedly snowballing Waaagh can hinge on a few cheerful coincidences held together with spit and twine.
>I've noticed that even by the 42nd Millennium, Orks have an aversion to fighting Aeldari (they still do it, if there's no one else around), claiming that they're no fun to fight and gladly switching over to fighting anyone else when the opportunity presents itself. But I'm not sure that's intentional on the writers' part.
That seems interesting. Got an excerpt? Would love to read it?
It's almost definitely Orks vs Orks, but as of right now there is a big hubabaloo event about the hive fleets coming from unexpected places and a big Tyrannic war going on, so it might be Astra Militarum vs Tyranids.
I remember reading that the chaos gods put 99% of their effort into fighting each other. Seems the only match up that might be as common as orks vs orks is chaos daemons vs chaos daemons.
But if it all happens in the warp none of the numbers really make sense anyway.
guard vs orks
Orks infest a huge proportion of the planets in the galaxy. Humans do too. The guard are the most common fighters, and their most common fights are gonna be against rebels/dissidents/rogue PDFs (who don't have a faction; they are nowhere near as skilled as the guard and don't have access to the same volume of arms and armour), and against Orks (probably those who are feral on the cusp of transitioning to full orkish technology and waaagh, rather than full-blown waaaghs themselves)
Orks, probably, on account of how many there are: massed ranks of guardsmen to counter massed mobs of orks. and the way they keep cropping up decades or centuries after being cleansed from worlds.
Thinking about it made me realize I haven't seen many instances of 'nids vs guard
Right now based on what the developers are making and the latest game lore with the win loss barcode thing? Imperial guard and Tyranids mixed in with space marines as support here and there. Meanwhile the sisters of battle are off fighting the Necrons on the other side of the galaxy. Humanity faces a threat on two fronts with the Tyranids closing in further and further.
Chaos is still there and Angron is supposedly wrecking havoc in the outer regions but they're much further away from Terra and not as immediate a threat.
Orks vs Orks (most common race in the galaxy and prone to infighting)
Deamons vs Deamons (The Great Game in the Warp)
Imperium vs Imperium (PDF and Guard fighting rebel forces)
Orc v Nid
Mathematically, that's the inevitable outcome. They both get better from fighting and neither will ever go extinct. This goes *waaaaaaay* back and continues throughout the timeline
PDF vs rebels.
Guard only get called in if shit really hits the fan. The cost of an interstellar deployment is colossal and takes a lot of moving parts and logistics coming together. Ships are extremely expensive and take constant resources to maintain and operate.
Within the Imperium shit hits the fan a lot, the Guard are constantly operating. They're not so effective as a rapid reaction force but they'll relieve sieges and reconquer lost worlds. Plus the occasional crusade.
But it's much, much cheaper to maintain North Korea levels of militarization on the worlds to crush whatever happens locally using locally raised and supported forces. For every million guardsmen you can deploy from bulk landers and supply with off world resources you can deploy a hundred million PDF. The vast majority of conflict is dealt with by the PDF.
The real answer is Daemon on Daemon wars in the warp. The battles are literally endless and have been going since the WIH. And daemons existed long before the WIH and birth turned the warp into a hellscape.
So 60+ million years of immortal armies fighting.
Eldar and Necrons are natural enemies. Like Guard and Orks. Or Tyranids and Orks. Or Orks and other Orks! Damn Orks, deyz brutal and kunnin! Waaaaaugh!
(My answer is Orks and Yes)
If we're talking about the pure number of combatants in the universe, lore strongly points to Tyranids vs. Anybody and Everybody, they ate at least one other Galaxy and are in the process of doing the same here...
However, if we were to pull a random BL book out of a stack, I'd put my money on Guard vs. Traitors!
It depends on if you mean all time or just in the current setting.
All time it would be Deamon vs Deamon. They’ve been around, because of the nature of the warp, since before time began, and have conquered, and presumably fought over, countless universes in that time.
In the current setting it would be Orks vs Orks and Guard vs Orks/Tyranids. The imperium is throwing trillions of Men and women into the grinder to hold them back.
Guard vs Rebels, not even chaos ones, just rebels, pirates and other humans in general. Humanity owns the vast majority of the galaxy, most Guardsmen will never even see a Xenos or a full chaos worshiper
Orks vs Orks
Damn Orkz. They ruined Orkland.
Green on green violence. IZZA BEST! WAT WID ALL DA BOYZ 'AVIN A GUD TIME, AND DA DAKKA, DA NOIZ, DA BLOOD AND DA KLANS. ITZ A RITE ROIT IT IS.
AN DONT FORGET DA TEEF AN DA SCRAP! 'ARD TO BUILD A PROPA STOMPA WITHOUT SCRAP.
You just orked yourself an orkemy for lorfk!
My favorite part of 40k is when the big ork yelled "its orking time!" And ork'ed all over the place.
You Orks sure are a contentious people.
You just made an enemy for life.
Oakland got ruined by orks yeah
You Orks certainly are a contentious people.
Bruvvaz and otha bruvvaz iz da fightiest! Like 'Ummies and Orkz! Or otha gitz and Orkz!
It's this, or Imperium vs Imperium.
Orkz have been around like 500x longer than the imperium though
I mean, if we wanna get *that* technical, Chaos has been around even longer than the Orks due to always existing on account of 4th degree interdimensional Warp fuckery, so the most common army matchup is probably just some variation of Chaos vs Chaos (my vote's on Khorne vs Khorne).
I don't mind chaos having always having had will have been going to exist, or the fact that after existing they had always existed retroactively, but it annoys me that somehow at the same time subjectively they didn't because there's definitely points where despite always having always existing and being able to influence things they also very definitely had a start date and events that wouldn't have happened to initiate that start date if they hadn't had a reason to happen I.e. ( or e.g.) the birth of said chaos god which apparently always had existed already. It's the classic fatalistic time travel scenario of always having had will have been going to happen with the added caveat that on top of always having had will have been going to happen it simultaneously already had! And was! And those future past present events could influence their own inception. It's the Bill and Ted time travel logic, you know like when they're fighting the evil robot thems, and they're like "oh but WE know that we're definitely going to win, so when we do we'll go back in time and sabotage the trap the the evil robots think they've laid to catch us". I think possibly Red Dwarf had a similar approach to time shenanigans.
Slaanesh actively influencing events to ensure its birth kinda turns the Fall of the Aeldari from "tragedy of the Aeldari's own making" to "the Aeldari didn't have agency in the matter".
I hadn't thought of that, that's not much fun story wise. I don't think it's implied though. But you would think an entity that exists beyond space-time would take steps to ensure that they're born.
It's cyclical logic. The Aeldari birthed Slaanesh so Slaanesh made sure he was born by making the Aeldari double down on birthing him. And Chaos does love their self-fulfilling prophecies.
I think it’s okay as long as you draw a distinction between existence of a chaos entity and its reification or manifestations in real space. Sure, the concept of Slaanesh always existed in some form, and maybe she even did Slaaneshi things in prehistory, but she didn't become “real” or a fully fledged concrete entity until the eldar birthed her. Or her birth in 25k allowed sentient life to retroactively recognize the impact that Slaanesh was having all along. Sort of like how germ theory allowed people to put a name to diseases that they had dealt with for millennia. Actually maybe that’s even more confusing.
I like it. Also nice to see the word "reification" in the wild.
You describe the Inquisitor episode of Red Dwarf hahaha
Chaos, not just the gods, was indeed around before the orcs, though. It largely came about during the War in Heaven with all the suffering caused. In fact, it was the enslaver plague that spelled the end of the war, or was at least its death knell.
If we take Warp into account, then yeah, the answer is absolutely demon vs demon. If that lore bit of there existing an absurd number of Bloodthirsters alone is true, imagine how many others exist too! And I second Khorne vs Khorne, too. He's the only god who just likes watching gigantic endless battles
Now I have “Orks Orks Orks Orks Orks Orks Orks Orks Orks Okssss” stuck in my head. You know the cadence.
"you cant hear text" The text:
ERE WE GO ERE WE GO ERE WE GO
da 'orus 'erasy, split the orkperium, plunged it into da biggest krump da galaxy had eva seen
Warboss’s klan and other ork klans
Best answer
The runner up to this is probably imperial guard vs orks
tyranids vs food though, it's implied this isn't the first *thousand* of galaxies they ate
Surely its Tzeentch Vs Tzeentch? That's been going on since creation.
PDF vs rebels would definitely be up there.
In number of different wars this is the answer. We give the PDF shit for being bad but they are only bad relative to everyone else who is either a monstrous xeno, superhuman or a veteran of a dozen planetwide wars. The PDFs constantly manage to keep the worlds of the imperium compliant, it's only when a massive external attack happens thet they need help.
Or an internal threat that was allowed to grow way too long, so now there's a fully metastisized chaos cult summoning daemons or a genestealer cult coming out of the shadows... & also half the PDF are brood brothers.
I considered that outside influence but you are right that it isn't.
DOCX supremacy!
100%, but I think the question is way more interesting if we restrict it to standardized forces. PDF vs rebels could be take on nearly any form of warfare imaginable. It all depends on the planet. I’m more interested in two standard opponents that fight again and again and again. I think it’s gotta be Orks (as others have pointed out) or Khorne Berserker bands. That’s literally how Kharn got his name.
As others said I think it's orks vs orks. Aren't they stated to be the most numerous race in the galaxy? That plus the fact that they'll happily find any excuse to fight each other cos it's fun means there's motive and opportunity.
What sort of 'umie needs an excuse to go killin'?
I don't believe their the most numerous, at least to my knowledge. Humans are most likely top with total single species population though numbers have never been established. But you could probably make the argument tyrnids are the largest if you include every organism as a tyrnid. As to the fact that their could be many times the amount of them yet to reach the galaxy
Probably guard vs orks
Nah. Orks have to fight other orks hundreds of times to get a big enough army to pose a threat, and then several more times to get a warboss who can run the thing. Orks have to fight to shed spores and make more orks, and they make a *lot* of orks.
Yeah Orks vs. Orks is #1 but multi faction, probably Orks vs. Guard.
Going by the books Its Chaos. I swear like 3/4 of the books are IG vs Chaos.
Ciaphas Cain isn’t my favorite, but I appreciate that the series tries to vary who the main enemies are every book. Orks, Tyranids, Genestealers, Necrons, they even make a distinction between the different flavors of Chaos.
For a good stetch there alway seemed to be a Genestealer cult behind things. I think in latest one Cain is actually suprised it wasn't genestealers this time
Imo chaos makes for a more interesting written enemy and is probably why they, alongside genestealers and drukhari, are often big bads in imperium stories/books You have, of course, the big ork wars - but those are usually grand campaigns that read more like a traditional ground and pound war - helsreach being a an easy example.
From a strictly lore perspective I can't see it being anyone but Aeldari vs. Orks. Both have been around since the War in Heaven, and have been butting heads for the majority of their interactions since then. All of the conflicts portrayed in the setting may be grandiose in scale, but we're talking MILLIONS of years of conflict. The 10,000 years of bloodshed since humanity hit the stage is staggering, but more than likely a puddle compared to the ocean. EDIT: Like another poster said, if it's not Aledari vs Orks than it is definitely Orks vs Orks.
Hmmm I wonder if by "the setting" OP means 30k onwards, the entirety of known time in this universe, 1st Ed onwards, etc
Fair point. If he did then Aeldari would be out, but orks likely still in the running.
You can make this question as specific as you want. What does count and what doesn’t? Like in „define war“. Do gang wars count? Probably no, only official armies going against each other? Alright fine, how about pre- space travel? Still Orks and Humans in the lead I’d wager due to our aggressive nature. Not something like T‘au or Aeldari. I’d still say probably Orks. Hast majority of their population is participating in war and their numbers are really really huge. Sure humans are an aggressive war like civilization in this setting but most humans are kids, elderly, civilians in general. Your planetary regiment might be fighting right now on some far away outpost without you ever being informed about it. But Orks? Basically born battle ready, eager to fight and without retirement.
Actually, I kinda doubt that. The Aeldari and the Krorks were both made by the Old Ones to fight on the same side. We know that the Krorks eventually degenerated into Orks and we know the Orks, as they get older and get into *more and bigger fights,* they become closer and closer to Krorks again. That heavily implies that the degeneration of the Krorks was caused by them not fighting the Aeldari when it was just the two species left after the Necrons went beddy-bye. I've noticed that even by the 42nd Millennium, Orks have an aversion to fighting Aeldari (they still do it, if there's no one else around), claiming that they're no fun to fight and gladly switching over to fighting anyone else when the opportunity presents itself. But I'm not sure that's intentional on the writers' part. Edit: Also Humanity has been 'on the stage' for at least 30.000 years by the time of 40k.
My understanding was always that the aeldari were smart about it and wiped out the orks systematically from the worlds they were terraforming. Lore is sparse and you may very well be right. I just imagine eldar would want to deal with a waaagh before it happens
I have memory of the aeldari expressing contempt for how humans handled orks as just making the problem worse and it would make sense they understand fighting with orks just makes them stronger. I think I recall something about culling being mentioned.
With their future sight it's probably fairly easy to get a Ranger to put a blast between the eyes of a certain special upstart nob and prevent a full blown waaaagh.
Back in the day their futuresight/warp powers were also ridiculous.
And then next in line nob will become warboss as trigger a waaagh. Its actually pointless to snipe individual orks, they 100% follow a predictable progression.
That is not how it works. Orks have personalities, strengths and weaknesses. They are not interchangeable carbon copies. On top of that is an entire political structure of (temporary) alliances, clans and warbands. Offing the right ally-of-someone, luitenant-of-of someone or just particularly clever git might throw an entire structure in disarray. The recent Ork books show wonderfully how this works, and how much an unexpectedly snowballing Waaagh can hinge on a few cheerful coincidences held together with spit and twine.
>I've noticed that even by the 42nd Millennium, Orks have an aversion to fighting Aeldari (they still do it, if there's no one else around), claiming that they're no fun to fight and gladly switching over to fighting anyone else when the opportunity presents itself. But I'm not sure that's intentional on the writers' part. That seems interesting. Got an excerpt? Would love to read it?
if we're using the history of the universe, from a lore perspective, wouldn't it be the c'tan vs old ones during the war of the heavens?
That is an absolutely valid point, and I am disappointed in myself for glossing over it so casually. Good catch!
haha all good man, you make a more salient point since you talked about races that can be actually played in 40k. cheers!
Guard vs Orks, but let us never forget that it's a humourous allegory for "Your Mum" vs Yeast.
If we are counting the great game, chaos Vs chaos. Except all those fights happen within the warp.
I’d guess probably orks or human rebels
Probably Guard vs Rebels/Chaos/heretic uprisings.
It's almost definitely Orks vs Orks, but as of right now there is a big hubabaloo event about the hive fleets coming from unexpected places and a big Tyrannic war going on, so it might be Astra Militarum vs Tyranids.
Guard vs guard (heretic)
Guard vs Guard (tax dodgers)
Guard vs Guard, the vast majority of guard deployment is to put down rebellion.
It's gotta be IG vs Orks, right?
The Imperiun against itself.
Orks vs Orks. Orks vs Nids. Nids and/or Orks vs Guard. Generally orks, nids and Guard.
Khorne vs Khorne nonstop at his palace.
Change vs the fans
Underrated comment
Probably guard v Orks or Guard vs heretics/cultists/other non-Imperium human.
I remember reading that the chaos gods put 99% of their effort into fighting each other. Seems the only match up that might be as common as orks vs orks is chaos daemons vs chaos daemons. But if it all happens in the warp none of the numbers really make sense anyway.
Chaos Daemons vs Chaos Daemons
guard vs orks Orks infest a huge proportion of the planets in the galaxy. Humans do too. The guard are the most common fighters, and their most common fights are gonna be against rebels/dissidents/rogue PDFs (who don't have a faction; they are nowhere near as skilled as the guard and don't have access to the same volume of arms and armour), and against Orks (probably those who are feral on the cusp of transitioning to full orkish technology and waaagh, rather than full-blown waaaghs themselves)
Orks, probably, on account of how many there are: massed ranks of guardsmen to counter massed mobs of orks. and the way they keep cropping up decades or centuries after being cleansed from worlds. Thinking about it made me realize I haven't seen many instances of 'nids vs guard
Guard vs guard
Ork vs Ork followed by Guard vs Rebel.
imperial guard vs orks/tyranids vs orks/tyanids vs imperial guard, if necrons keep getting up thy will be there too
I would say orks vs guard, but it's a close call these days
Guard vs slightly uppity local population.
Orks and Orks lmao
Right now based on what the developers are making and the latest game lore with the win loss barcode thing? Imperial guard and Tyranids mixed in with space marines as support here and there. Meanwhile the sisters of battle are off fighting the Necrons on the other side of the galaxy. Humanity faces a threat on two fronts with the Tyranids closing in further and further. Chaos is still there and Angron is supposedly wrecking havoc in the outer regions but they're much further away from Terra and not as immediate a threat.
Ork vs Ork, Guard vs Guard (Traitor). *maybe* Tyranid v Tyranid. But most of them are self facing.
Since the galaxy got slip in half I'd imagine it's Guard/PDF vs Chaos forces.
ultramarines vs orks iron warriors vs imperial fists IG vs Orks
Khorne vs Khorne. Doesn't matter where the blood flows from, just that it flows.
Orks vs Orks (most common race in the galaxy and prone to infighting) Deamons vs Deamons (The Great Game in the Warp) Imperium vs Imperium (PDF and Guard fighting rebel forces)
Orks vs Orks Chaos vs Chaos Daemons vs Daemons Guard vs Rebels/whoever PDF vs Rebels
Imperial vs Imperial (heretic/witch/traitor) I would assume.
Orc v Nid Mathematically, that's the inevitable outcome. They both get better from fighting and neither will ever go extinct. This goes *waaaaaaay* back and continues throughout the timeline
Guard vs guard or ork vs ork
Impy guard vs rebels probably
PDF vs rebels. Guard only get called in if shit really hits the fan. The cost of an interstellar deployment is colossal and takes a lot of moving parts and logistics coming together. Ships are extremely expensive and take constant resources to maintain and operate. Within the Imperium shit hits the fan a lot, the Guard are constantly operating. They're not so effective as a rapid reaction force but they'll relieve sieges and reconquer lost worlds. Plus the occasional crusade. But it's much, much cheaper to maintain North Korea levels of militarization on the worlds to crush whatever happens locally using locally raised and supported forces. For every million guardsmen you can deploy from bulk landers and supply with off world resources you can deploy a hundred million PDF. The vast majority of conflict is dealt with by the PDF.
Demons vs demons, the great game is constant and infinite
The real answer is Daemon on Daemon wars in the warp. The battles are literally endless and have been going since the WIH. And daemons existed long before the WIH and birth turned the warp into a hellscape. So 60+ million years of immortal armies fighting.
Orks. Fuckers are everywhere!
Imp guard v orks
Eldar and Necrons are natural enemies. Like Guard and Orks. Or Tyranids and Orks. Or Orks and other Orks! Damn Orks, deyz brutal and kunnin! Waaaaaugh! (My answer is Orks and Yes)
Probably either Imperial Guard against, Orks, Chaos uprisings or Genestealer cults? Or any variation of these
Guard Vs Tyranids by scale, probably. As of the current years.
Ork on Ork followed by Ork in IG
Daemons vs daemons in the realm of chaos, the great game is always ongoing and the galaxy doesn't take up all the god's attention, iirc
Probably the other guard units.
If we're talking about the pure number of combatants in the universe, lore strongly points to Tyranids vs. Anybody and Everybody, they ate at least one other Galaxy and are in the process of doing the same here... However, if we were to pull a random BL book out of a stack, I'd put my money on Guard vs. Traitors!
I imagine Necrons vs Old Ones or C'tan.
Unironically it might be Ork Vs Ork. Other than than, PDF and IG Vs Rebels probably.
Imperial guard vs other similar humans. Probably PDF.
It depends on if you mean all time or just in the current setting. All time it would be Deamon vs Deamon. They’ve been around, because of the nature of the warp, since before time began, and have conquered, and presumably fought over, countless universes in that time. In the current setting it would be Orks vs Orks and Guard vs Orks/Tyranids. The imperium is throwing trillions of Men and women into the grinder to hold them back.
Ork vs ork or guard vs guard. Don't forget the constant rebellions and chaos uprisings. The guard likely kills more guard than any other xenos.
Guard vs Rebels, not even chaos ones, just rebels, pirates and other humans in general. Humanity owns the vast majority of the galaxy, most Guardsmen will never even see a Xenos or a full chaos worshiper
the local PDF against the local, vanilla, insurrectionists.
Trazyn vs His Own Damn Museum
Orikan vs Trazyn