Is it possible for the Imperium to ally with Chaos humans against Craftworld Eldar?

[casb1965]

Not a chance, the Imperium would fight both simultaneously rather than ally with Chaos, it's worst enemy.

[diadems]

1 hour ago, casb1965 said:

Not a chance, the Imperium would fight both simultaneously rather than ally with Chaos, it's worst enemy.

 

speaking of the Imperium's worst enemy, actually i realized that the relationship between the Imperium's chaophobia and xenophobia has never really been explored

 

though there are stories about the humans ceasing their hostilities with each other to beat back the greenskins, which also shows that things aren't so clear cut

Edited January 4 by diadems

[Halandaar]

2 hours ago, diadems said:

well i think its plausible that there could be transactional imperial commanders who could agree to a ceasefire in order to conveniently collectively kick some xenos butt and then just as easily ruthlessly turn on the traitors when they're no longer needed

 

Assuming any given Imperial commander is even able to think outside their conditioning, propaganda and religious dogma to the point they'd consider an alliance of convenience with a Chaos-aligned force, they still have to contend with the reality that Chaos draws the eye of the Inquisition, and that isn't going to end any better for them than being shredded by shurikens.

 

And this is assuming they can even get their forces to go along with them without getting assassinated; even in the War of the Beast example you've cited, a chunk of Zerberyn's marines turn against him and he only gets out of it by killing a Black Templar Marshall and pledging himself to Kalkator

 

It simply isn't possible to do things like this on a "transactional" basis. In the Imperium, once you've allied with traitors, you are a traitor too. 

 

 

[diadems]

14 hours ago, Halandaar said:

they still have to contend with the reality that Chaos draws the eye of the Inquisition, and that isn't going to end any better for them than being shredded by shurikens.

 

hmm, well the Inquisition does worry about xenos as well

 

 

14 hours ago, Halandaar said:

And this is assuming they can even get their forces to go along with them without getting assassinated; even in the War of the Beast example you've cited, a chunk of Zerberyn's marines turn against him and he only gets out of it by killing a Black Templar Marshall and pledging himself to Kalkator

 

yeah, though wasn't this after the Ork threat had subsided? so they did have transactional attitudes which helped to revise their misgivings about ceasing fire with Chaos forces

 

 

14 hours ago, Halandaar said:

It simply isn't possible to do things like this on a "transactional" basis. In the Imperium, once you've allied with traitors, you are a traitor too.

 

hmm well maybe not exactly allying, but just having a ceasefire, to stop shooting each other while they both shoot Asuryanis

 

and Imperial men are also not above negotiating ceasefires with Chaos even without the presence of third party threats, like in the event that the Chaos force is not belligerent at the moment and the Imperial force is too weak to take on it or even has a chance of being destroyed itself

Edited January 5 by diadems

[Kommisar_K]

The Imperium has allied with xenos against Chaos (recent notable examples include Armageddon & Bobby G's return) but I personally cannot remember any Imperium Chaos alliances that turned out... mutually beneficial. Alpha legion could definitely infiltrate an imperial force and aid them. Though they'd probably have a very different goal in the long-term. 

You mention ceasefires as opposed to full-on alliances. I want to explore that. Let's try a very basic (and possibly ridiculous) scenario. 

Spoiler

Let's say we've got Cadians and cultists fighting in a city. Reports of Eldar attacking the cultist lines reach the Cadian commander as cultists start to withdraw from fortified positions. Let's say they pick up a lot of enemy vox chatter about a massive Eldar force razing everything in its path. The Cadian commander sees the xenos as an additional threat to the city and a more powerful one than the cultists. With the cultists & Eldar already fighting, the Cadians decide to outflank the Eldar. This way they can eliminate a strong enemy even as that enemy wears down, and is worn down by, the other enemy force. Assuming the Eldar are defeated, the Imperials can continue straight on to mow down whatever cultists remain afterwards. 

This represents a situation where Chaos and Imperium could have an non-negotiated ceasefire of sorts. In this scenario, they're fighting the same enemy, but they're working independently, keeping each other at arms length. And of course, the end goal is to kill each other along with the xenos. So, very short term. 

Repercussions; The Inquisition will probably look into an event like this. To escape burning at the stake, the Cadian commander will need to prove the strategy was really the best, possibly even disregarding casualty counts. Also, if the strategy failed in the first place, that commander gets executed by a Commissar right then and there, no question. 

 

I've got absolutely no idea how Chaos/Imperials could maintain a successful campaign-long alliance.

 

[Magos Takatus]

I personally think most people in the Imperium would consider the stain of those that have personally betrayed them would always be a greater insult than the deeds of the Aeldari. It's quite possible to be betrayed by the Eldar and have a grudge, but when one of your own spits on their oaths, it's much more personal, at least as I would expect anyway. Maybe you could wrangle a scenario but it would feel somewhat contrived to me unless the Imperium didn't know the renegades were aligned with Chaos in the first place.

[diadems]

On 1/10/2026 at 4:42 PM, Magos Takatus said:

I personally think most people in the Imperium would consider the stain of those that have personally betrayed them would always be a greater insult than the deeds of the Aeldari. It's quite possible to be betrayed by the Eldar and have a grudge, but when one of your own spits on their oaths, it's much more personal, at least as I would expect anyway. Maybe you could wrangle a scenario but it would feel somewhat contrived to me unless the Imperium didn't know the renegades were aligned with Chaos in the first place.

 

as in, the idea is that the Imperium is already xenophobic, and about how detestable the Asuryani are to them

 

and also I guess that the Horus Heresy Traitors didn't really betray mankind to xenos races

 

there's also a passage that might make Horus seem more xenophobic than the Loyalists and make it seem like a cause of the Horus Heresy:

Quote

The Emperor’s great armies have served their purpose. Now is the time for the Legions to be disbanded and the Space Marines set to other tasks guarding the worlds of humanity and policing the new regimes. The warrior lords that are the primarchs are to become the rulers of worlds and administrators of the Grand Plan.

 

Horus seeks vengeance! He wants to rid the galaxy of mankind’s alien foes utterly. Not a single alien should remain alive to threaten humanity. The Legions must hunt them down and eradicate them all! The glorious armies of the Imperium should not be forced to put down their guns and swords. They must not be emasculated and converted into mere policemen and gatekeepers! The daemon argues a clever and compelling case in Horus’ ear and the Emperor should beware the serpent!

 

Edited January 13 by diadems

[diadems]

On 1/10/2026 at 2:48 AM, Kommisar_K said:

The Imperium has allied with xenos against Chaos (recent notable examples include Armageddon & Bobby G's return) but I personally cannot remember any Imperium Chaos alliances that turned out... mutually beneficial. Alpha legion could definitely infiltrate an imperial force and aid them. Though they'd probably have a very different goal in the long-term. 

You mention ceasefires as opposed to full-on alliances. I want to explore that. Let's try a very basic (and possibly ridiculous) scenario. 

  Hide contents

Let's say we've got Cadians and cultists fighting in a city. Reports of Eldar attacking the cultist lines reach the Cadian commander as cultists start to withdraw from fortified positions. Let's say they pick up a lot of enemy vox chatter about a massive Eldar force razing everything in its path. The Cadian commander sees the xenos as an additional threat to the city and a more powerful one than the cultists. With the cultists & Eldar already fighting, the Cadians decide to outflank the Eldar. This way they can eliminate a strong enemy even as that enemy wears down, and is worn down by, the other enemy force. Assuming the Eldar are defeated, the Imperials can continue straight on to mow down whatever cultists remain afterwards. 

This represents a situation where Chaos and Imperium could have an non-negotiated ceasefire of sorts. In this scenario, they're fighting the same enemy, but they're working independently, keeping each other at arms length. And of course, the end goal is to kill each other along with the xenos. So, very short term. 

Repercussions; The Inquisition will probably look into an event like this. To escape burning at the stake, the Cadian commander will need to prove the strategy was really the best, possibly even disregarding casualty counts. Also, if the strategy failed in the first place, that commander gets executed by a Commissar right then and there, no question. 

 

I've got absolutely no idea how Chaos/Imperials could maintain a successful campaign-long alliance.

 

 

hmm interesting

or maybe something simpler,

like, in a particular region of space, Asuryani forces come into conflict with both Imperial and Chaos-human forces at the same time, and the two human forces decide not to shoot at each other while they fight against the Asuryani because they think that the Asuryani represent a more serious threat

[Magos Takatus]

4 hours ago, diadems said:

 

as in, the idea is that the Imperium is already xenophobic, and about how detestable the Asuryani are to them

 

and also I guess that the Horus Heresy Traitors didn't really betray mankind to xenos races

 

there's also a passage that might make Horus seem more xenophobic than the Loyalists and make it seem like a cause of the Horus Heresy:

 

The excerpt speaks to me that this deamon is trying to use Horus' fears that he won't have a purpose after the Great Crusade has ended? He's following the Emperor's intentions to the letter, but questions whether once the fighting is over, he will be reduced to a mere politician, or worse, he may share the same fate as the Thunder Warriors? I don't see this as being any more xenophobic than the rest of the Imperium, just that the Emperor won't need him once the fighting ends. You can't have a Warmaster without a war to master.

[Jolemai]

It's an Emperor TTS sketch, but the only thing the Imperium and Chaos have in common in Xenophobia...

[diadems]

1 hour ago, Magos Takatus said:

The excerpt speaks to me that this deamon is trying to use Horus' fears that he won't have a purpose after the Great Crusade has ended? He's following the Emperor's intentions to the letter, but questions whether once the fighting is over, he will be reduced to a mere politician, or worse, he may share the same fate as the Thunder Warriors? I don't see this as being any more xenophobic than the rest of the Imperium, just that the Emperor won't need him once the fighting ends. You can't have a Warmaster without a war to master.

 

hmm i thought the passage is quite explicit

 

Quote

Horus seeks vengeance! He wants to rid the galaxy of mankind’s alien foes utterly. Not a single alien should remain alive to threaten humanity. The Legions must hunt them down and eradicate them all!

 

15 minutes ago, Jolemai said:

It's an Emperor TTS sketch, but the only thing the Imperium and Chaos have in common in Xenophobia...

 

Lol

and well the Eldar are also particularly anti-Chaos which raises the ire of Chaos forces who also happen to be humans

Edited January 13 by diadems

[Magos Takatus]

18 hours ago, diadems said:

 

hmm i thought the passage is quite explicit

 

 

 

Lol

and well the Eldar are also particularly anti-Chaos which raises the ire of Chaos forces who also happen to be humans

I feel by highlighting that quote you are ignoring the entirely of the quote and the meaning behind it to focus on the one sentence that supports your aim? I could provide a quote that not only proves that elements of the Imperium hold the same view as Horus did, and equally want heretics and traitors exterminated as well:

 

"A Monodominant is a member of a Puritan faction of the Inquisition that believes in the philosophy known as Monodominance; namely, that the only way the Imperium of Man may survive is if every other faction in the galaxy -- xenos, Chaos or Heretic -- is destroyed. To the Monodominant, there can be no tolerance of heresy, no matter its degree or kind, and the only possible punishment for heresy is death. Monodominant Inquisitors are utterly ruthless, unforgiving, and militant. They will meet any form of sin or deviation with swift and final judgement."

 

I'm not saying this scenario is impossible, however, I am saying that being betrayed by a supposed ally is typically a far deeper wound than by a stranger. The Emperor wanted to unite humanity to protect them from the predations of Xenos, and the betrayal of the Horus Heresy destroyed that dream forever. To a citizen of the Imperium, it's the fault of Chaos that the Eldar still live to be a threat in the first place. Of course, the typical citizen of the Imperial would know very little of the Horus Heresy, but one fact remains, they view humans that support the Ruinous Powers to have betrayed the Emperor, and only a fool would put any trust in a traitor. It would be like trying to get an honest answer to a question out of the Alpha Legion.

 

I think the biggest problem with an Imperial/Chaos ceasefire against a Xenos threat is that in 40k as soon as you let the door to Chaos open, it lets itself in. Once an Imperial faction gives an inch in tolerating corruption, it typically starts a clock to their own downfall, so it stops becoming the story of how an Imperial and Chaos faction allied against the Asuryani, and more a story of how Imperials fell to Chaos while under attack from the Eldar. I think that's the biggest problem you'll have here.

 

Saying that, now I've got to try to help you think of an engaging and plausible way how it *could* happen. 

[diadems]

3 hours ago, Magos Takatus said:

I feel by highlighting that quote you are ignoring the entirely of the quote and the meaning behind it to focus on the one sentence that supports your aim? I could provide a quote that not only proves that elements of the Imperium hold the same view as Horus did, and equally want heretics and traitors exterminated as well:

 

as in, i was just trying to bring up the point that the Horus Heresy Traitors didn't really mean to betray mankind to xenos races

 

 

 

3 hours ago, Magos Takatus said:

I am saying that being betrayed by a supposed ally is typically a far deeper wound than by a stranger.

 

hmm ok, like earlier you mentioned the Eldar committing betrayal and that kinda confused me a bit

 

 

3 hours ago, Magos Takatus said:

I think the biggest problem with an Imperial/Chaos ceasefire against a Xenos threat is that in 40k as soon as you let the door to Chaos open, it lets itself in.

 

hmm what kind of goal would the problem be against?

[Magos Takatus]

19 minutes ago, diadems said:

 

as in, i was just trying to bring up the point that the Horus Heresy Traitors didn't really mean to betray mankind to xenos races

 

 

 

 

hmm ok, like earlier you mentioned the Eldar committing betrayal and that kinda confused me a bit

 

 

 

hmm what kind of goal would the problem be against?

Okay, I am starting to understand what you were getting at better. I was just thinking from the perspective of an Imperial citizen or soldier. What little they would know of the Aeldari is that the are capricious and untrustworthy, so they would expect to be betrayed by the Aeldari if they put any trust in them, and if they did ally with them and get betrayed, it's because they trusted Xenos in the first place. Their xenophobia means their default stance is that the alien should not be trusted.

 

By comparison, the Imperium would view Chaos as fellow humans that have betrayed them, they were on the same side and they blame the traitors for turning their backs on the Imperium. They trusted them and that trust was betrayed. They expected to be betrayed by xenos, but they did not expect to be betrayed by fellow humans, which is why I think they tend to hate them that much more.

 

Of course, this is only the Imperial Perspective, the Aeldari and "traitor" perspectives would of course be very different. The Aeldari don't seem to have a strong opinion of humanity, they fall to Chaos easily (ironic, really) but they do recognise that some humans strive to fight against the ruinous powers as much as they do (The rare example of an Inquisitor being permitted into the Black Library). I can't really generalise about Chaos perspectives because they seem to be less indoctrinated than the Imperium and in their case it's more about personal grievances in a lot of cases. Bitter space marines, cults rejecting Imperial oppression, temporary alliances and betrayals with other factions etc.

 

As for the final point, could you clarify that, please? I don't understand what you are communicating. I'm not sure if it's the way you worded it, me being tired, or just a lack of comprehension on my part.

[diadems]

On 1/14/2026 at 11:14 PM, Magos Takatus said:

Okay, I am starting to understand what you were getting at better. I was just thinking from the perspective of an Imperial citizen or soldier. What little they would know of the Aeldari is that the are capricious and untrustworthy, so they would expect to be betrayed by the Aeldari if they put any trust in them

 

so my point in bringing up the lore quote was that any beef between the Loyalists and the Traitor marines might not really affect the Imperium's anti-xenos position

 

 

On 1/14/2026 at 11:14 PM, Magos Takatus said:

As for the final point, could you clarify that, please?

 

so you said: "I think the biggest problem with an Imperial/Chaos ceasefire against a Xenos threat is that in 40k as soon as you let the door to Chaos open, it lets itself in.".

 

and i was just thinking, problematic or not, i was wondering whether it would be possible for a ceasefire against Craftworld Eldar

[Dr. Clock]

Imperials that ally with known non-Imperial humans are, by definition, heretics. So maybe a commander 'calls truce' with a Chaos army to pursue xenos, but as soon as they do, by definition they are also at that point effectively Excommunicate Traitoris. They might not think of themselves as such, so it could and probably does happen, but it would be exceedingly rare for them to not eventually be found out or just fall directly to Chaos. I'd certainly have... questions about their loyalty going forward from that kind of rupture, because any Imperial commander and their sub-commanders and commissariat/chaplains will know that allying with Chaos is the same as being corrupted by it.

 

So most likely it would seem more common for Chaos 'allies' to be just pretending to be Imperials, at least as far as their direct communications and appearance to the true Imperial commanders in the field. One convenient thing about war theaters in 40k is that they are really, really big. A war against Eldar might be coordinated across great distances and even across the entirety of the Cicatrix, so communications with 'forces on the other end' of the webway routes a xenos faction is protecting might be able to communicate only by means of Astropaths, and thus it wouldn't be much of a stretch for Chaos agents of suitable power to effectively just 'pretend to be Imperial astropaths' and coordinate a common response to a common threat without anyone ever actually laying eyes on their 'allies' directly. Eldar themselves well know that it's generally easier to deceive Imperials than to tempt them from their strange corpse-creed. 

 

Cheers,

 

The Good Doctor. 

[kabaakaba]

 

22 minutes ago, Dr. Clock said:

Imperials that ally with known non-Imperial humans are, by definition, heretics. So maybe a commander 'calls truce' with a Chaos army to pursue xenos, but as soon as they do, by definition they are also at that point effectively Excommunicate Traitoris. They might not think of themselves as such, so it could and probably does happen, but it would be exceedingly rare for them to not eventually be found out or just fall directly to Chaos. I'd certainly have... questions about their loyalty going forward from that kind of rupture, because any Imperial commander and their sub-commanders and commissariat/chaplains will know that allying with Chaos is the same as being corrupted by it.

 

So most likely it would seem more common for Chaos 'allies' to be just pretending to be Imperials, at least as far as their direct communications and appearance to the true Imperial commanders in the field. One convenient thing about war theaters in 40k is that they are really, really big. A war against Eldar might be coordinated across great distances and even across the entirety of the Cicatrix, so communications with 'forces on the other end' of the webway routes a xenos faction is protecting might be able to communicate only by means of Astropaths, and thus it wouldn't be much of a stretch for Chaos agents of suitable power to effectively just 'pretend to be Imperial astropaths' and coordinate a common response to a common threat without anyone ever actually laying eyes on their 'allies' directly. Eldar themselves well know that it's generally easier to deceive Imperials than to tempt them from their strange corpse-creed. 

 

Cheers,

 

The Good Doctor. 

I'm agreed. ANY weakness open way to more. Here you truce with chaos, there you think they not that bad guys, and after few more little steps you wear red uniform and steel visage on face and shouting "Blood for the blood god". It's simplified version but it's work this way. Once your faith and armor of contempt cracks, you are doomed.

 

Regarding astropaths that not this simple. Astropaths marked. Any message have codes and engrams so you can't just falsifying it or say you are new astropath.

 

[Dr. Clock]

23 hours ago, kabaakaba said:

Any message have codes and engrams so you can't just falsifying it or say you are new astropath.

Sure, yep, in most cases. I'm not saying it'd be easy or common, just easier from a narrative standpoint to be 'deceived at a distance' by a canny Chaos agent of some kind. Once you're relying on timey-wimey Warp stuff you're on Chaos home turf anyhow, I figure.

 

Cheers,

 

The Good Doctor.

[Antarius]

Imperials, whether Space Marines or regular humans turn to Chaos all the time. Allying against xenos in order to eke out a win (or just survival, which is a pretty strong motivation for less-than-ideal acts) might just be the first step, so I see no reason this couldn’t happen, depending on the circumstances - but it’d be very dangerous, of course.

[Teetengee]

it's also important to remember that most regular people within the 40k imperium don't have a functional working knowledge of what chaos is, what it looks like, what its followers do or how they work. It's so coached in propaganda, and there is so much variability within imperial forces, that it is perfectly reasonable for imperials to not even realize a chaos force *is* a chaos force. In fact, it's possible for huge swaths of chaos troops to not realize *they* are chaos aligned. So with all that said, I could see a truce being made against craftworld eldar with "that damned tax evading guerrilla network who have infuriatingly good prescience when it comes to predicting where enemy forces will strike," maybe even offering a penal legion type deal of looking aside at the previous indiscretions so long as the eldar are destroyed and they quit rebelling after. Alternatively, if an imperial force were fighting and a space marine force dropped to support them, they wouldn't necessarily realize that force was chaos aligned (particularly if one of the more practical chaos forces, like alpha legion or iron warriors). The longer any such alliance went, the more likely it would be that the imperials realize who they are working with, but at least for single or limited campaign engagements, where chaos is keeping quiet about their proclivities, it's possible.

I suspect it would usually end in some combination of:
a. the imperials corrupted, turning to chaos
b. the inquisition assuming a and glassing the planet
c. the same situation that happened when tau tried allying with drukhari

[Tempest0518]

I don't think there's any situation where the Imperium even for a slight amount of time would be willing to ally with Chaos and I'm certain Chaos would not do the same either.

[The Praetorian of Inwit]

What about the Hrud? They were brutal even for a Legion with their Primarch. Or the mega arachnids from Murder?