I know that permanent alliances in the WH40k universe are impossible, all races are too prejudiced, too proud, or just too mindless to achieve such an alliance. In the grim, dark future of the 41st Millenium there is only war.

However, there are situations where members of two (or more) races have to work together for a common goal. While they inevitably split and/or betray each other, they, for a time, fight together, plan together, and have to place limited trust in one another.

Massive operations (entire armies/fleets working together) hold most value to this question, but even single individuals would count, and the longer an alliance lasted, the more valuable it is here.

And one condition: cases where members of one race ditch their original affiliation don't count, for example, humans leaving the Imperium to join the Tau wouldn't count here.

  • I'm not able to recall the specific chapters or craftworlds, but there a quite a few examples of Eldar and Space Marines working together, usually to tackle Chaos or Tyranids.
    – Daft
    Commented Apr 16, 2016 at 12:05
  • What are you looking for exactly? A list of examples?
    – Taladris
    Commented Apr 16, 2016 at 12:45
  • @Taladris not exactly. More like a trend that stems from these examples? I want a straight up answer, like "Xs and Ys have the easiest time cooperating, because reasons. They cooperated here and there, more often than others, "
    – Petersaber
    Commented Apr 16, 2016 at 12:56
  • I've reworded the question a little. This shouldn't leave anything to opinions.
    – Petersaber
    Commented Apr 16, 2016 at 18:40

3 Answers 3


That might be a cheating answer to your question but what we call the Tau empire is actually made from many allied races, two of the most common ones are Tau and Kroot, the latter is also known to work as a mercenaries for anyone who is willing to pay, including Chaos.

If you ask about the information from the tabletop game, here is a helpful diagram: enter image description here Which kinda agrees with what you can read in the books - eldars are the one that are most likely to give a hand to someone, usually for their own gain (especially the Harlequins, which are sort of masters of themselves focused on fighting Slaanesh) and are known to cooperate with almost everyone (except for Chaos, Necrons and obviously Tyranids).

Second place (or maybe even first?) would go to...Orks, especially the Freebooterz, that are happy to deal with almost anyone for the loot and the fun of Waaaagh (and contrary to the picture above, they have been working with humans as well).

  • While this doesn't specify examples of alliances, this answer is as close as you can get to a complete one. Since the WH40k Universe is directly connected to the tabletop game, it's reasonable to expect the books and games follow this. I am surprised that the Tau and the Imperium are only "desperate allies", but I guess it's either Greater Good or annihilation.
    – Petersaber
    Commented Apr 17, 2016 at 16:05
  • 1
    @Petersaber its matter of politics: relationships between Mankind and Tau can be compared to situation from the height of Cold War between USA and USSR. Yes, they can sit down and talk (Ciaphas Cain series had few examples of such cooperation), but in the end you have two empires that want to expand their borders. Also in last years of M41 Tau broke the peace treaty and started expansion against Empire.
    – Yasskier
    Commented Apr 17, 2016 at 20:17

The Necrons formed temporary alliances a few times when it benefits them, note though they did not need to do this in order to win they did it so as not to waste their own ships/resources.

Word of the Silent King by LJ Goulding

Most recent example of the Necrons is in the Gehenna Campaign. The Necrons under Szarekh the Silent King formed an alliance with the Blood Angels and Dante to stop a Tyranid hive fleet, though this was after the Necrons attacked the world in question to setup a trap to easily defeat the Tyranid fleet but the Blood Angels interfered costing the Necrons time and resources. The Silent King left the Blood Angels to the front lines and only intervened when needed to stop the Tyranids, costing the Blood Angels massive losses while preserving much of his own forces.

The Silent King had met Sanguinius, the primarch of the Blood Angels, and had great respect for him; he believed a true alliance between the Necrons and Imperium could have been formed if Sanguinius had not fallen. Its unknown if the Silent King would have helped another chapter of space marines.

Perhaps, had he not fallen to illogical and prideful infighting, their Sanguinis-Angel might have steered them towards a more enlightened destiny. Certainly, he would have made a more amenable emperor than a preserved witch-corpse. If ever there were a human to be mourned, noble Szarekh would say it was him. That alliance - the first alliance, perhaps?

There is another example of the Necrons helping the Tau against the Tyranids but this could not really be called an alliance. The Tyranids attacked a Tau world which was a tomb world. The Necrons woke up, killed the Tyranids and left the Tau alone. After the battle, when the Tau went to thank them, the Necrons flayed them and killed everything left on the planet.


Eldar and Space Marines / the Inquisition have worked together on numerous occasions

I'm having trouble locating the exact stories but Eldar and Space Marine fight side by side when a greater threat arises.

I remember a story in which a small number of Space Marines, Eldar and Chaos Space Marines land on the same moon in search of some ancient artifact. Eldar and Space Marine work together to stop the Chaos Space Marines. Once the Chaos Marines are defeated, the humans betray the Eldar right before the Eldar planned on betraying the humans.

Space Marines in general have a lot of respect for the Eldar warriors but betrayal is a common theme when any alliance is formed.

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