Warhammer 40k Archives

A Galaxy Unmanned by Angels: An Introduction to an Imperium Without Astartes

The Adeptus Astartes, the Space Marines, stand as the iconic “Angels of Death” in the grim darkness of the 41st Millennium. They are the Emperor’s ultimate sanction, bio-engineered transhuman warriors forming the spearhead of His armies, pivotal in the Imperium’s founding and its desperate, ongoing survival. Their towering forms, clad in power armour and wielding boltguns, are synonymous with the might and terror of the Imperium. To imagine a Warhammer 40,000 universe without them is to envision a reality fundamentally altered, where the very bedrock of Imperial power and narrative is reshaped. Their absence would not merely be a missing unit type on the grand battlefield of the galaxy; it would signify a profound divergence in the Emperor’s grand design and the subsequent history of mankind.

This exploration delves into that great “What If”: a Warhammer 40,000 universe where the Astartes project either failed catastrophically, was never conceived by the Emperor and his gene-wrights like Amar Astarte, or was deemed an impossible dream. The ramifications would be immense, triggering a cascade of profound changes. Such a shift would reshape the Great Crusade from its inception, alter the nature and leadership of any galaxy-spanning civil war, necessitate entirely new military doctrines, and forge a different, though perhaps still grimly recognizable, Imperium of Man by the 41st Millennium. The very strategy of the Emperor, whose genius supposedly crafted the Astartes as the key to reconquering the galaxy, comes under scrutiny. If this cornerstone of His plan was absent, it suggests either a monumental failure in His foresight or that He was compelled to pursue a significantly compromised path from His “ideal” vision of galactic conquest and human reunification. This could lead to an Imperium that, from its very birth, was forced to rely more heavily on the diverse, unaugmented talents of humanity, mass mobilization, or perhaps even riskier technological or alternative augmentation pathways.

Navigating this speculative timeline requires grounding in the established lore of other Imperial factions and historical precedents within the 40K universe. What follows is an exploration of possibilities, a journey into an alternate Imperium, forged without its transhuman demigods.

The Great Crusade: A Mortal Tide Forges an Empire

The Great Crusade, the Emperor’s ambitious campaign to reunite the scattered worlds of humanity, would have unfolded with a dramatically different character without the Legiones Astartes. The spearhead of this galactic reconquest would need to be composed of other forces, each with their own strengths and inherent limitations.

The Emperor’s Armies Reimagined: Who Fills the Void?

The Thunder Warriors: A Lingering Shadow or a Necessary Evolution?

The Thunder Warriors were the Emperor’s first generation of gene-enhanced soldiers, instrumental in the Unification Wars on Terra. They were canonically described as physically stronger, more savage, and more potent in combat than even the later Astartes. However, their creation was deeply flawed; they suffered from severe genetic instability, leading to dangerous mental breakdowns, berserker rages where they might attack friend and foe alike, and early metabolic collapse, with organs sometimes spontaneously detonating under stress. Their lifespans were brutally short.

Without the Astartes as a viable, more stable replacement, the pressure to refine or, at least, mass-produce the Thunder Warriors would have been immense. The Emperor and his gene-wrights, including figures like Amar Astarte, might have been forced to pour resources into attempting to stabilize their genetic structure. Could a “Mark II” or “Mark III” Thunder Warrior have emerged – perhaps less overwhelmingly powerful than the originals but more disciplined and longer-lived? If stabilization proved impossible, the Emperor might have had no choice but to use them as a brutal, short-term shock force, accepting their high attrition rate and the constant drain on resources and morale. The Great Crusade would have begun, therefore, with an elite warrior caste known for its severe limitations. The logistical and ethical burden of maintaining legions of these unstable, dying giants would have been considerable, potentially fostering a more cynical and pragmatic approach to warfare from the Imperium’s outset. These warriors, visibly flawed and terrifying, would have shaped the early Imperium’s image more through fear than the awe sometimes inspired by Astartes. The eventual, canonical “culling” of the Thunder Warriors at Mount Ararat would become an even more precarious event if no superior replacement like the Astartes existed. It could have led to deep-seated mistrust within the nascent Imperial military if the reasons were not transparent or if the forces intended to succeed them were perceived as inadequate. Conversely, had they been successfully stabilized, they might have formed a powerful, entrenched warrior caste, presenting its own set of political challenges to the Emperor’s rule.

Adeptus Custodes: From Guardians to Reluctant Generals?

The Adeptus Custodes, the Emperor’s personal guard, the “Ten Thousand,” represent the pinnacle of genetic and martial perfection, warriors of unmatched skill and loyalty. However, they were never intended to be a conquering army; their primary role was the defense of the Emperor and the Imperial Palace on Terra. Their numbers, though formidable for their role, were always limited – canonically around ten thousand at their inception, though reduced by conflicts such as the War in the Webway.

In an Imperium without Astartes, the temptation to deploy these peerless warriors more broadly would be immense. While not a direct replacement for entire legions, small contingents of Custodes might have been used more frequently for critical, high-stakes objectives where sheer quality was paramount, or perhaps to act as advisors and commanders for elite mortal forces. Their presence on a battlefield would be a significant morale booster for Imperial troops and a terrifying portent for any enemy. However, their limited numbers would always severely constrain their strategic impact. Any increased deployment of Custodes to active war fronts would also mean that Terra itself, and the Emperor, would be less defended – a monumental risk. This could have led to the development of specialized Custodes command cadres or rapid-response “troubleshooting” teams, distinct from their traditional bodyguard duties, but they would always remain a highly constrained and precious resource, their deployment a matter of grave strategic calculation.

The Imperialis Auxilia (Imperial Army): The True Hammer of Mankind

Canonically, the Imperialis Auxilia, later known as the Imperial Army, formed the vast bulk of the Great Crusade’s military strength. These mortal soldiers and their myriad regiments provided the numbers necessary to hold conquered territory, conduct large-scale planetary assaults, and support the Astartes’ spearhead actions. As one source notes, “the meat and bones of the Crusade was made up of the Imperial Army”. Their equipment varied wildly, from advanced weaponry on par with elite formations to more primitive gear from less developed worlds, and they were typically subordinate to Astartes command structures when operating in joint campaigns.

In a scenario devoid of Astartes, the Imperial Army would unequivocally become the primary offensive and defensive force of the Great Crusade. Its sheer size, logistical capacity, and the diversity of its regiments would be even more central to Imperial strategy. The quality, training, and equipment of its regular line regiments might see significantly greater investment. The command structure of the Imperial Army would be entirely human, potentially leading to different strategic priorities and doctrines. Without Astartes shock troops to break enemy resistance, a greater emphasis would likely be placed on meticulous combined arms warfare, overwhelming artillery barrages, and massed infantry assaults as the primary means of achieving victory. The leadership, no longer deferring to Primarchs or Legion Masters for the most dangerous undertakings, would see the rise of its own class of highly influential mortal generals, whose experiences and doctrines would shape Imperial military tradition in a distinct fashion.

The Solar Auxilia: Ascendant Elite of Mortal Humanity

The Solar Auxilia were canonically the elite of the Imperial Army, highly trained and exceptionally well-equipped mortal soldiers, hardened for void warfare and combat in the most hazardous environments. They were capable of fighting alongside the Legiones Astartes or, crucially, in place of them when the Legions were overstretched or unavailable. One source indicates they comprised about a quarter of the Imperialis Auxilia’s void-faring strength, numbering several thousand regiments, with another suggesting approximately 10,000 cohorts by the Crusade’s height.

Without the Astartes, the Solar Auxilia would undoubtedly ascend to become the Imperium’s premier fighting force, the undisputed “Angels of Death” crafted from baseline humanity. Their numbers would likely see significant expansion, and investment in their advanced wargear – such as their signature void-sealed armour and potent lasrifles – and rigorous training regimens would be paramount. They would become the public face and practical embodiment of Imperial elite warfare. This elevated status would likely lead to the Solar Auxilia developing more specialized sub-formations to cover the diverse and demanding roles that Astartes Legions filled, such as heavy breakthrough assaults, rapid flanking maneuvers, and complex void combat operations. However, their casualty rates in the high-intensity conflicts that defined the Great Crusade would be immense, far exceeding those of transhuman Astartes. This would necessitate a vast and continuous recruitment and training pipeline, drawing the best and brightest from across the compliant worlds to replenish their ranks. As the undisputed human elite, the Solar Auxilia could develop a powerful institutional identity and wield considerable political influence. Their Lord Commanders and Marshals might become figures of immense renown and authority, akin to the later Chapter Masters of Astartes Chapters, potentially forming a distinct and powerful bloc within the Imperium’s military and political landscape. Their unique martial cultures and traditions, noted for their discipline and somewhat archaic appearance, would become even more pronounced and central to the overall Imperial military identity.

The Mechanicum’s Might: War Machines and Cybernetic Legions

The Mechanicum of Mars, even before its formal alliance with the Emperor, possessed formidable military power. This included the Skitarii legions – cybernetically augmented warriors – Knight Houses with their agile war machines, and the colossal god-engines of the Collegia Titanica, which had served as the Mechanicum’s primary military arm.

In an Imperium reliant on mortal and Mechanicum forces, the direct military contribution of Mars to the Great Crusade would likely be even greater. There might be a more pronounced emphasis on the large-scale deployment of Skitarii legions as elite infantry formations, and an even heavier reliance on Knight Banners and Titan Legions to provide the overwhelming firepower and shock action necessary to break heavily fortified enemy worlds or counter large xenos war-constructs. This increased military indispensability could grant the Mechanicum even more leverage over the nascent Imperium. The terms of the Treaty of Olympus, which formalized the alliance between Terra and Mars, might be skewed further in Mars’s favor. Imperial commanders on the front lines might find themselves more dependent on the cooperation and specialized knowledge of Mechanicum Magi for critical battlefield support, from logistical chains for advanced munitions to the deployment of unique technological assets. Furthermore, the absence of Astartes as the Emperor’s premier super-soldiers might have spurred the Mechanicum to more vigorously pursue its own alternative super-soldier programs. This could involve developing more advanced and widespread cybernetic augmentation for human warriors, pushing the boundaries beyond standard Skitarii capabilities, or perhaps even creating sophisticated combat automata if the Emperor’s canonical ban on Abominable Intelligence was less stringent or interpreted differently in this altered timeline.

The Pace and Nature of Galactic Compliance

The Great Crusade, without the lightning-fast, decisive assaults often spearheaded by Astartes Legions, would likely have been a significantly slower and more attritional undertaking. One analysis suggests that while the Emperor could have conducted the Crusade without Astartes, it might have taken a thousand years or more, rather than the roughly two centuries it canonically did. Victories would be harder-won, relying more on protracted sieges, massed artillery bombardments by the Imperial Army, overwhelming assaults by Solar Auxilia cohorts, and the devastating power of Titan Legions to crack the defenses of resistant worlds. The “tip of the spear”, while still sharp in the form of the Solar Auxilia, would be blunter overall and require a much larger shaft of supporting forces to drive it home.

This altered dynamic could lead to more worlds being brought into compliance through negotiation, vassalage, or protracted diplomatic efforts, as the option for rapid, overwhelming conquest becomes less consistently feasible. The Imperium, by the time any major internal schism erupted, might therefore be smaller, less consolidated, or composed of more diverse political arrangements than the canonically Astartes-forged realm. The slower pace of expansion might also grant hostile xenos empires more time to recognize the growing threat of humanity, consolidate their own power, or form alliances, making later stages of the Crusade even more challenging. Similarly, human pocket empires that had survived Old Night might become more deeply entrenched and thus harder to dislodge.

Early Xenos Conflicts: Ullanor and the Rangdan Xenocides

Critical campaigns against major xenos threats, such as the Ork Empire of Urlakk Urg at Ullanor or the terrifying Rangdan Xenocides, would have been even more devastating for Imperial forces. The Rangdan Xenocides, which canonically pushed multiple Astartes Legions to the brink of annihilation and beyond, might have been unwinnable in a no-Astartes scenario, or resulted in such a pyrrhic victory that the Great Crusade was crippled for decades, its momentum shattered. The conquest of Ullanor, the crowning achievement of the Great Crusade, would have required an even greater concentration of mortal forces – Solar Auxilia, Imperial Army regiments beyond counting – and the full might of Mechanicum war engines to overcome the sheer ferocity and numbers of the Orks.

The psychological toll on mortal soldiers facing such existential horrors without the reassuring presence of the “invincible” Astartes would be immense. Imperial propaganda would need to work tirelessly to maintain morale, perhaps focusing on the exceptional heroism of Solar Auxilia commanders, the unyielding discipline of the Imperial Army, or the awe-inspiring power of the Titan Legions. The sheer weight of casualties among the elite Solar Auxilia and veteran Imperial Army units could lead to “lost generations” of the Imperium’s finest mortal soldiers, impacting its ability to prosecute further campaigns and potentially forcing a more defensive strategic posture much earlier in its history. This could also necessitate the more frequent use of extreme measures, such as virus bombing or cyclonic torpedoes, to achieve victory against intractable foes, further shaping the Imperium’s grim reputation across the galaxy.

Table: Comparative Elite Forces in the Great Crusade (No Astartes Scenario)

The Age of Heresy: A Different Betrayal, A Different War

The galaxy-spanning civil war known as the Horus Heresy was defined by the betrayal of nine Primarchs and their Astartes Legions. Without Astartes, the very nature of such a cataclysmic conflict would transform, though the potential for widespread rebellion and the insidious influence of Chaos would remain ever-present.

The Primarch Question: Did They Exist? If So, What Was Their Purpose?

Canonically, the twenty Primarchs were created by the Emperor using His own genetic material to be the generals and progenitors of the twenty Space Marine Legions. Their gene-seed was the very foundation upon which each Legion was built. Their existence is thus intrinsically tied to the Astartes project.

Speculation Path A: Primarchs Exist.

If the Primarchs were created, but the Astartes project subsequently failed or was never viable, their intended purpose would be radically altered. These demigod figures, possessing superhuman intellect, charisma, and martial prowess, would still be formidable assets. The Emperor might have assigned them as supreme commanders of vast Expeditionary Fleets composed of Imperial Army and Solar Auxilia forces, or as governors-general of entire sectors of the expanding Imperium. In this scenario, their inherent ambitions, complex personalities, deep-seated rivalries (such as that between Perturabo and Rogal Dorn), and, crucially, their susceptibility to the temptations of Chaos could still manifest. A supremely charismatic and influential Primarch, a Horus Lupercal equivalent, could still rally other disaffected Primarchs and the mortal armies under their direct command to rebellion against the Emperor. The resulting Heresy would then be a “Primarchs’ Civil War” fought between colossal armies of baseline humans, elite Solar Auxilia, and Mechanicum cohorts, all led by demigods on both sides. The scale of destruction might be even greater due to the sheer numbers of mortal soldiers involved in these continent-spanning battles and system-wide fleet actions, even if individual engagements lacked the focused, transhuman intensity of Astartes clashing with Astartes. The focus of such a war would be on grand strategy, the loyalty of entire sectors swayed by Primarch charisma, and the control of vast logistical networks, rather than the iconic Legion-versus-Legion engagements of the canonical Heresy.

Speculation Path B: No Primarchs.

Alternatively, if the Astartes project was deemed impossible from its very inception, the Primarch project itself might have been abandoned or never reached full fruition. The Emperor, lacking these twenty “sons,” would have to rely on exceptionally gifted human commanders – perhaps elevated Lord Commanders of the Imperial Army or Marshals of the Solar Auxilia – and the established civilian and military command structures like the Council of Terra to manage the Great Crusade and govern the Imperium. In this reality, a Heresy-level event would likely stem from different sources. It could be a council of powerful, ambitious mortal Lord Commanders seeking to carve out their own empires, a deepened and more widespread schism within the Mechanicum (the canonical Schism of Mars demonstrates their capacity for large-scale internal conflict and siding with rebellion), or perhaps widespread rebellion by numerous disaffected sectors chafing under Terran rule or the imposition of the Imperial Truth. The leadership of such a rebellion would be vastly different, lacking the singular, demigod figures of the Primarchs, and might instead be a fractious coalition of warlords or ideologues. Chaos, ever opportunistic, would undoubtedly seek to exploit and exacerbate such divisions.

The Seeds of Rebellion: Catalysts for Civil War Without Transhuman Legions

Even without transhuman Legions and their demigod Primarchs, the seeds of a galaxy-wide civil war could find fertile ground within a mortal-led Imperium:

• Ambitious Mortal Commanders: The Lord Commanders of the vast Expeditionary Fleets of the Imperial Army and the highest-ranking officers of the Solar Auxilia would control immense military resources and manpower across sprawling regions of space. Such power, coupled with the isolation of deep-galaxy campaigns, could easily foster separatist ambitions, resentment towards Terran dictates, or provide tempting targets for Chaos corruption. The sheer scale of the Imperial Army meant its highest commanders held power comparable to provincial governors of old, with armies to enforce their will.
• Mechanicum Schisms: The Adeptus Mechanicus was, and is, a power unto itself. The canonical Schism of Mars during the Horus Heresy saw a significant portion of the Mechanicum, including Fabricator-General Kelbor-Hal, ally with Warmaster Horus, driven by desires for forbidden knowledge, resentment of the Emperor’s restrictions on research (such as into AI), and theological disputes about the nature of the Omnissiah. Such a schism could easily occur in a no-Astartes timeline, perhaps aligning with powerful mortal rebel leaders or even becoming the primary instigator of the civil war. A Mechanicum-driven Heresy might focus more on technological supremacy, the unrestricted pursuit of archeotech, and the overthrow of Terran constraints on their research. Battle lines would be drawn between “loyalist” and “dark” Mechanicum factions, each commanding their own Skitarii legions, Knight Houses, and Titan Legions, and dragging the rest of the fledgling Imperium into their devastating conflict.
• Ideological Dissent & The Imperial Truth: The Emperor’s enforced atheism, known as the Imperial Truth, and His later restrictions on the use of psychic powers (culminating in edicts like the Council of Nikaea) were sources of contention even among the Primarchs and Astartes. Within a broader mortal populace, these policies could breed significant resentment, particularly on worlds with long-standing spiritual traditions or where psykers were integral to their society. Ambitious figures, whether military commanders or planetary governors, could rally those who chafed under Imperial rule, using ideological grievances as a banner for rebellion. The absence of Astartes, some of whom (like the Word Bearers) became the most fervent apostles of Chaos after initially championing the Emperor’s divinity, would shift the primary vectors for large-scale Chaos corruption. Entire Solar Auxilia cohorts or Imperial Army commands, perhaps disillusioned by endless war, resentful of Terran oversight, or directly tempted by promises of power from the Ruinous Powers, might become the main conduits for daemonic influence and the core of “traitor armies,” rather than transhuman demigods and their legions. The nature of Chaos cults might also be different, perhaps more deeply embedded within the regular human populace or mainstream military structures from an earlier stage, exploiting mortal frailties like despair, ambition, and fear on a grander scale.

Chaos Undivided: Exploiting a Mortal Imperium

The Ruinous Powers would undoubtedly seek to exploit any divisions within a mortal-led Imperium. Baseline humans, and even the elite of the Solar Auxilia, might be considered more susceptible to certain forms of subtle corruption, despair, or the insidious promises of power than the psychologically conditioned and genetically altered Astartes. While Astartes often fell due to grand flaws like hubris, immense psychic power, or profound disillusionment (as seen with Magnus the Red), the fall of mortal leaders and their followers might be a more insidious, creeping process, driven by more common human failings.

However, a mortal Imperium might also possess unique strengths against Chaos. The sheer, unshakeable faith of the masses, if properly cultivated and directed by a strong, centralized Imperial Cult (which would likely rise to prominence, especially in the aftermath of a Heresy), could become a potent spiritual weapon. The absence of super-powered individuals like Primarchs might mean fewer “single points of catastrophic failure” for Chaos to target and corrupt to trigger galaxy-spanning betrayals.

The nature of daemonic incursions and Chaos cults would likely adapt. Instead of elite Chaos Space Marines and Possessed Astartes forming the vanguard of Chaotic assaults, the Imperium might face more widespread daemonic possession amongst its own mortal troops or entire planetary populations turning to dark worship. The strategies to combat Chaos would rely less on specialized elite daemon-hunters (as no Grey Knights equivalent would exist from this era) and more on massed displays of faith, brutal purges conducted by loyal Imperial Army units or, later, forces like the Adepta Sororitas, and the sheer weight of numbers to contain and eradicate outbreaks of Chaotic influence. The concept of “daemonifuges,” psychic wards, and anti-psyker measures might become even more critically important for elite mortal units expected to face the horrors of the Warp.

The 41st Millennium: An Imperium Forged in Mortal Struggle

Ten thousand years after a galaxy-altering civil war, an Imperium without Astartes would be a vastly different entity, yet likely still locked in the same desperate struggle for survival. Its military, society, and technological trajectory would all bear the imprint of this fundamental absence.

The State of Imperial Military Power: The Unyielding Mortal Bulwark

• The Imperial Guard (Astra Militarum) and Imperial Navy: These forces would be, even more so than in canonical lore, the undisputed backbone and primary fighting instrument of the M41 Imperium. Their doctrines would heavily emphasize massed formations, overwhelming firepower from artillery and armored columns, and intricate combined arms operations with robust Imperial Navy support for void superiority and planetary assault. The Guard might be even more diverse than canonically depicted, with a greater proliferation of highly specialized regiments attempting to fill the myriad tactical niches that Astartes Chapters might otherwise have covered (e.g., dedicated heavy siege regiments, rapid-assault drop troops, void combat specialists). These could be direct inheritors of the varied traditions of the Great Crusade-era Imperial Army. The status and influence of Lord Generals, Lord Marshals, and Solar Admirals would be immense, these mortal commanders holding the fate of entire sectors in their hands.
• Successors to the Solar Auxilia: Guardians of Elite Tradition? The elite Solar Auxilia of the Great Crusade, with their advanced wargear and void-hardened training, would likely leave a lasting legacy. It is conceivable that their traditions would survive 10,000 years, evolving into elite, heavily armed and armored regiments within the Astra Militarum, or perhaps even a distinct fighting arm. These “Solar Successors” would function as super-Kasrkin or Grenadiers, forming the core of any major offensive, acting as a strategic rapid reaction force, and tackling the most dangerous assignments. They might retain access to superior void-sealed power armor and advanced weaponry, setting them apart from standard Guard formations. These warriors would be the Imperium’s most revered mortal soldiers, symbols of human martial excellence at its peak. Their recruitment and training would be incredibly rigorous, drawing from the best candidates across entire sectors, and their numbers, while limited compared to the Guard as a whole, would be strategically vital. They would be the closest the Imperium could come to “human Astartes,” the benchmark against which all other mortal soldiers are measured.
• Adeptus Mechanicus: The Indispensable Forges of War: The reliance on the Adeptus Mechanicus for advanced weaponry, war machines, and technological expertise would be absolute. Skitarii legions, Knight Houses, and the god-engines of the Collegia Titanica would be even more critical for providing the heavy firepower and specialized technological warfare capabilities that an Imperium without Astartes would desperately need. This heightened dependency could translate into even greater political power for the Mechanicus. Any major military campaign requiring significant technological assets would necessitate their deep involvement, potentially giving the Tech-Priests of Mars veto power over strategic decisions or allowing them to pursue their own arcane agendas more freely, demanding access to lost archeotech or data from battlefields as recompense for their aid.
• Adepta Sororitas: The Ascendant Shield of Faith: The Adepta Sororitas, the Sisters of Battle, canonically rose to prominence following the Age of Apostasy in M36, a period of intense civil strife and religious turmoil. In a timeline without Astartes, their role as an elite, power-armored, and fervently faith-driven fighting force might have been recognized and expanded much earlier, or they might become even more central to Imperial military doctrine post-Apostasy. It is plausible that the Sororitas would be far more numerous and influential, their Orders Militant taking on many of the roles that Astartes Chapters (particularly zealous ones like the Black Templars or those with strong religious convictions) would have fulfilled. They would be a common sight on battlefields across the Imperium, especially in conflicts against the forces of Chaos, xenos cults, and internal heresy. The relationship between the Ecclesiarchy (the state church of the Imperium) and the broader Imperial military might be more deeply intertwined, with Sororitas detachments routinely assigned to Imperial Guard armies to bolster morale and provide elite shock troops. The “Acts of Faith” performed by the Sisters, fueled by their collective belief, and the awe-inspiring presence of Living Saints – individuals seemingly blessed with miraculous powers by the Emperor – would be even more crucial for maintaining the morale of mortal soldiers and achieving battlefield breakthroughs against seemingly insurmountable odds.
• Officio Assassinorum: The Blade in the Shadows: The unique and terrifying skills of the Officio Assassinorum in targeted elimination would be of even greater strategic importance. Without Astartes vanguard units or specialized strike forces to perform decapitation strikes against enemy leaders, disrupt command structures, or neutralize high-value targets, the Imperium would rely more heavily on its assassins. The High Lords of Terra might authorize deployments from the various Assassin Temples – the chameleonic Callidus, the peerless marksmen of the Vindicare, the berserk Eversors, and the anti-psyker Culexus – more frequently. This would make the Officio Assassinorum a more active, albeit still deeply clandestine, player in shaping the outcome of Imperial conflicts, their operatives turning the tide of wars with a single, perfectly executed kill.
• The Void Left by Specialized Astartes (Grey Knights, Deathwatch): The absence of hyper-specialized Astartes formations would leave critical vulnerabilities.
  • No Grey Knights: The Imperium would lack a dedicated, psychically potent, and incorruptible Astartes-equivalent force specifically designed to combat the daemonic. This is a catastrophic deficiency. The Ordo Malleus of the Inquisition would be forced to rely more heavily on its own highly trained and specially warded Inquisitorial Stormtroopers, select units of exceptionally faithful Adepta Sororitas, and perhaps attempt to develop cadres of exceptionally powerful and rigorously controlled Sanctioned Psykers specifically for anti-daemonic warfare. The risk of corruption among these forces would be immense. It is conceivable that the Adeptus Custodes, if any survived a Heresy-equivalent in sufficient numbers and with an expanded mandate beyond the Sol System, might be forced to develop a small, hyper-elite anti-daemonic contingent, though this would stretch their already limited resources to breaking point.
  • No Deathwatch: The specialized anti-xenos role, involving the study and targeted eradication of diverse alien threats, would fall to elite veteran formations drawn from Solar Successor regiments or highly experienced Imperial Guard units. These ad-hoc forces would likely operate under direct Inquisitorial Ordo Xenos oversight, granted access to specialized wargear and intelligence. However, the ability to rapidly adapt tactics and counter wildly diverse xenos physiologies and technologies would be significantly slower and more costly in lives and resources than with a dedicated, adaptable force like the Deathwatch. The Imperium’s institutional understanding of daemonic entities and esoteric xenos threats might consequently be less developed. The constant, brutal learning curve against such foes would be paid for in oceans of mortal blood. This could lead to a more paranoid and reactive Imperium, quicker to resort to the ultimate sanction of Exterminatus when faced with threats it cannot easily understand or counter with its conventional mortal forces.

Technological Trajectory: A Different Path of Innovation and Stagnation?

The absence of Astartes would ripple through the Imperium’s technological landscape. The unique role of Techmarines, who bridge the cultural and technological gap between Astartes Chapters and the Adeptus Mechanicus, maintaining their Chapter’s specialized wargear, would not exist. Consequently, Astartes-specific technologies like their bespoke power armor patterns and the bolter as a widespread transhuman-scaled standard weapon would not have been developed or disseminated in the same way.

Elite mortal forces, such as the Solar Successors or the Adepta Sororitas, would likely utilize power armor and advanced weaponry sourced more directly from, and maintained by, the Adeptus Mechanicus. This could lead to more standardized designs for elite wargear across the Imperium, perhaps lacking the individual customization and Chapter-specific relics seen in Astartes armories, but potentially easier to produce and maintain on a larger scale.

The vast resources – material, intellectual, and temporal – poured into creating, equipping, and sustaining the Legiones Astartes and their successor Chapters would be freed. This raises several possibilities for their reallocation. Could this lead to greater investment in advanced Imperial Guard and Imperial Navy wargear, uplifting the capabilities of the common soldier and starship? Might it fund more ambitious (and potentially more dangerous) research projects within the Adeptus Mechanicus, leading to forgotten technological breakthroughs or, equally likely, more catastrophic techno-heresies? Or would these resources simply be absorbed by the inevitably increased attrition rates of mortal forces fighting wars without transhuman support?

The general technological stagnation of the Imperium is a core theme of the 40K setting, a slow decay from the heights of the Dark Age of Technology. Without the Astartes, who sometimes act as custodians of ancient technology or are instrumental in the rediscovery of lost STC fragments, this stagnation might be exacerbated in certain areas. However, the pressing need to equip elite mortal forces to a higher standard to face existential threats might, paradoxically, drive localized innovation or encourage a wider dissemination of existing advanced technologies that were previously hoarded or restricted. The overall aesthetic of Imperial warfare might also change significantly. There would be less focus on the iconic, bulky silhouette of the Space Marine, and more on diverse human troopers clad in various patterns of advanced, but distinctly human-scaled, power armor and environmental gear, alongside a greater visual and battlefield presence of Mechanicum war constructs, from Skitarii phalanxes to towering Knight walkers and god-machine Titans.

The Imperial Cult and Societal Morale: Faith in a Mortal Imperium

The absence of the Emperor’s “Angels of Death” would profoundly affect how the Master of Mankind and His Imperium are perceived by the countless trillions of Imperial citizens. The unique blend of awe and terror inspired by the physical presence of Astartes would be missing from the Imperial psyche.

In such an Imperium, the Imperial Cult – the state religion centered on the worship of the God-Emperor – might become even more central to societal cohesion, spiritual resilience, and the maintenance of morale. The deeds of Living Saints, heroic Imperial Guard commanders, distinguished Marshals of the Solar Successors, and selfless Canonesses of the Adepta Sororitas would be amplified by Ecclesiarchal propaganda, becoming the primary exemplars of Imperial virtue and martial prowess. The average Imperial citizen’s hope, when faced with the overwhelming horrors of the galaxy, would rest squarely on the shoulders of ordinary (albeit exceptionally brave and often well-equipped) human beings, and on the distant, divine figure of the enthroned Emperor. This could foster a different kind of resilience, one born of shared mortal struggle and collective faith, or perhaps lead to even deeper wells of despair when that faith is tested beyond its limits. The Ecclesiarchy’s power could become even more absolute, with faith deployed as the primary psychological weapon against fear, dissent, and heresy. Cults of personality around specific, widely revered saints or martyr-generals might become incredibly widespread and powerful, potentially leading to their own internal religious schisms or rivalries within the broader Imperial Creed.

Enduring the Unending War: Humanity’s Stand Against Key Xenos and Chaos

Without Astartes, the Imperium’s methods for confronting its myriad existential threats would adapt, relying on the strengths and accepting the limitations of its mortal and Mechanicum defenders.

• Ork WAAAGHs!: Confronting the green tide would necessitate a strategy of layered defense, relying on heavily fortified lines, massed artillery and armor support from the Imperial Guard to attrite Ork numbers, and stringent Naval blockades to prevent reinforcements. Decisive assaults to break Ork leadership, particularly targeting powerful Warbosses who galvanize the WAAAGH!, would fall to elite Solar Successor formations and powerful Mechanicus battle groups. The primary challenge would be containing the sheer ferocity and overwhelming numbers of a major WAAAGH! without Astartes shock troops to conduct surgical strikes against key Ork command structures or execute lightning breakthroughs in the Ork lines. Such campaigns would be incredibly costly in mortal lives.
• Tyranid Hive Fleets: Victory against the Great Devourer would hinge on the Imperial Navy’s ability to engage and destroy Tyranid Hive Ships in void combat before they can make significant planetary landfall. Ground wars against Tyranid swarms would be nightmarish battles of attrition. The Imperial Guard would be tasked with holding vast defensive lines, while Solar Successors and Mechanicus units would be deployed to counter larger, more dangerous bio-forms like Carnifexes or Hierophants. A key tactical objective would be to sever the Hive Mind’s Synapse network by targeting synapse creatures. The greatest challenge lies in the Tyranids’ relentless adaptation and their ability to recycle biomass. Without Astartes to perform rapid, high-risk decapitation strikes against critical Synapse creatures or to conduct hazardous boarding actions against Hive Ships, breaking the Hive Mind’s control and halting the consumption of a world’s biosphere would be exceptionally difficult. The immense loss of Guardsmen biomass would, horrifically, fuel the Tyranid advance even more rapidly.
• Necron Awakenings: Facing the ancient and technologically supreme Necrons would demand overwhelming firepower to destroy their metallic bodies faster than their reanimation protocols can take effect. Elite human forces would need to exploit the Necrons’ often rigid adherence to protocols and lack of individual initiative (among lower ranks) with dynamic and unorthodox tactics. Targeting awakening Tomb complexes with sustained orbital bombardment or deploying specialized Mechanicus archeotech-weaponry would be crucial. The primary challenge is the vast technological disparity. Necron gauss weaponry can strip atoms from armor, and their regenerative capabilities make them incredibly durable. Without the enhanced resilience and specialized wargear of Astartes, mortal forces would suffer horrific casualties. Fully neutralizing an active Tomb World’s core infrastructure would require immense resources and almost certainly the direct intervention of powerful Mechanicus forces.
• The Archenemy – Chaos: The fight against the insidious forces of Chaos would be a constant, grinding war on multiple fronts – internal and external. The Inquisition would maintain eternal vigilance, rooting out cults and corruption. Purges would be conducted by fanatically loyal Adepta Sororitas and proven Guard regiments. Containing daemonic incursions would rely on massed displays of faith, the firepower of consecrated weaponry, and the desperate efforts of Sanctioned Psykers to provide psychic defense and offense. The core challenge is the pervasive and insidious nature of Chaos corruption, which preys on mortal weakness, and the sheer resilience of daemonic entities. Without a force like the Grey Knights, major daemonic entities and Greater Daemons would be almost impossible to banish permanently from the material realm, their defeat often temporary and incredibly costly. Wars of Faith against Chaos-tainted worlds or invading forces would be brutal, total, and unending.

Across all these threats, the Imperium’s strategic doctrine would likely become inherently more defensive and reliant on attrition. The concept of “Exterminatus” – the complete destruction of a planet’s biosphere – might be employed more readily as a final solution when conventional mortal forces are overwhelmed or when facing threats deemed too dangerous to contain. The value of individual elite soldiers – Solar Successor officers, Sororitas Canonesses, Officio Assassinorum operatives – would be incredibly high, their survival and effective deployment paramount to Imperial strategy.

Table: M41 Imperial Defenses – Key Threats & Primary Responders (No Astartes Scenario)

A Different Grim Darkness, But Darkness Nonetheless

The absence of the Adeptus Astartes would not merely remove a faction from the Warhammer 40,000 universe; it would fundamentally rewrite its history and reshape its character. The Great Crusade would have been a slower, more brutal slog, led by the elite mortals of the Solar Auxilia and the war machines of the Mechanicum, its victories paid for in oceans of human blood. Any subsequent galaxy-wide Heresy might have been driven by the ambitions of powerful mortal commanders or deep schisms within the Martian Priesthood, rather than the fall of transhuman demigods.

By the 41st Millennium, this alternate Imperium would rely utterly on the unyielding mass of the Imperial Guard, the specialized elite of Solar Auxilia successor formations, the fervent faith and firepower of the Adepta Sororitas, and the indispensable technological might of the Adeptus Mechanicus. The Officio Assassinorum would be an even more crucial scalpel, while the lack of specialized Astartes like the Grey Knights would leave gaping wounds in the Imperium’s defenses against the daemonic and the truly esoteric xenos.

Would this Imperium be stronger, weaker, or simply different? It would undoubtedly be more reliant on sheer numbers, raw faith, and the brute application of conventional firepower. It might be less prone to the specific, catastrophic failings born of transhuman hubris and the immense power wielded by individual Astartes and their Primarchs. Yet, it would also lack their unique strengths – their resilience, their speed, their capacity for surgical, overwhelming force. The quote attributed to Custodian Captain-General Trajann Valoris, that the Imperium is ultimately held together not by Astartes or Custodes but by its common people, would resonate with an even more profound truth in this reality. The triumphs and tragedies of humanity would be played out on an entirely mortal scale, albeit one stretched across a million worlds and ten millennia of unceasing war.

The core themes of Warhammer 40,000 – endless war, the necessity of sacrifice, the fragility of civilization against a hostile galaxy, and the insidious, ever-present threat of Chaos – would likely remain, perhaps even intensified. The darkness would have a different texture, the heroes and villains different faces, but the fundamental, desperate struggle for humanity’s survival would persist. The absence of the Emperor’s Angels means that humanity itself, in all its flawed, courageous, and often desperate forms, must stand as its own, and only, shield against the encroaching night. The grim darkness of the far future would endure, perhaps even deepened by the knowledge that no transhuman saviors are coming – only more ordinary men and women, standing shoulder to shoulder against the terrors of the void.