The latest edition of Warhammer: The Horus Heresy brings a streamlined and flexible system for fielding allied forces, making it easier than ever to mix factions in your army list—without needing to wade through layers of obscure restrictions or confusing keywords. While the lore behind these alliances is rich and compelling, let’s focus on what the new mechanics mean for players and how they might affect your army-building and gameplay decisions.
The Core Concept: Flexible Allied Detachments
In this edition, allies are handled as optional Allied Detachments that are simply plugged into your army structure. The only hard rule is that allied detachments must come from a different faction than your main army. That’s it.
Each allied detachment follows a familiar force org chart—nothing is mandatory, and you don’t even need to include troops if you don’t want to. You can take as many of these detachments as your command slots allow, with one major limitation: allied units must account for no more than 50% of your total points.
That cap prevents abuse while still offering considerable freedom. You can easily run a 3,000-point game with 1,500 points dedicated to a completely different faction, which is substantial in Horus Heresy terms.
Command Slots and Auxiliary Unlocks
Each Command slot in your army allows you to include an additional Auxiliary Detachment. If you’re running a mainline detachment with a Praetor, you can potentially unlock all the tools of that faction’s arsenal—Elites, Retinues, and more. However, you’ll miss out on High Command characters, Primarchs, and other apex options. These are exclusive to your Warlord’s faction, which makes sense—narratively and for balance.
This means you can field a competent and characterful allied force, but it will always feel like a supporting element, not a full army-within-an-army. That balance is key.
Lords of War Detachments: Bring the Big Guns
The Lords of War Detachment stands apart. It lets you bring in up to 25% of your army’s points worth of Lord of War units—from any faction. That means your Iron Hands force could include a Mechanicum Knight, or your Word Bearers could call in a Warhound Titan. Want to run a Fellblade without devoting an entire detachment to it? This is how.
This structure gives players a clean and elegant way to integrate super-heavy units or try out new centerpieces without breaking narrative or balance.
Why This Matters for Players
From a gameplay perspective, these rules open the door for more varied, thematic, and strategic builds without requiring complex hoops to jump through. Whether you’re running a narrative campaign or prepping for a large multiplayer game, you can now represent the sort of coalition warfare the setting is famous for.
From a hobby standpoint, it’s a godsend. Want to dip your toes into Solar Auxilia, Custodes, or even the Mechanicum without starting from scratch? Build a 750–1,000 point allied detachment. It’s enough to showcase a few key models, get a taste of painting a new faction, and still see play.
Our Take
This is one of the best systems introduced in the current edition. It respects the structure and balance of Horus Heresy, while giving players more creative freedom. The hard 50% point limit and exclusion of key HQs like Primarchs ensure that your main force remains the narrative and tactical centerpiece.
For those who enjoy modeling and painting, it’s also a perfect on-ramp to a second or third force—without the guilt of starting yet another army that let's face it, you may not get around to finishing. We are all guilty of that here too.
This system isn’t just more inclusive—it’s more fun. And at the end of the day, that’s what a good ruleset should be.
Whether you’re building a thematic Shattered Legions force or just want an excuse to add a Saturnine Dreadnought to your collection, these new Allied Detachment rules deliver flexibility without sacrificing structure. We’re fans.