And now for the counter-argument. If you're looking for the first part in favour of the legions and bringing up the flaws in implementing chapters, you can find it here. That done, on with the article!
Arguments In Favour of the Formation of Space Marine Chapters
So now we've covered the many points surrounding the weaknesses and criticisms of breaking up the legions into thousand man chapters. Suffice to say many have probably heard these many times over and perhaps even agree with them. They certainly seem to be repeated far often both by loyalist and traitor players alike, yet for all of this the advantages are all too often overlooked. Many of these keep focusing upon how each force can be far more easily picked off, and there is a degree of truth there. However, at the same time few seem to ever truly recognise the preventative measures or differences in combat doctrine between then and now.
Of all the threats facing the Imperium at the dawn of M32, the biggest of these was the threat of corruption. Having faced a previously unknown foe capable of attacking them from within and beyond, the once mighty empire had suffered a massive betrayal, just by corrupting a few key figures. By targeting the primarchs, the ingrained loyalty and dutiful nature of the astartes meant they would fall into line easily.
This is best seen with the contrast between Horus and Khan in the novels False Gods and Scars. As Horus fell, almost all the legion fell into line with him. Even those who had been outside the Warrior Lodges were quick to accept his new direction, even turning against the Emperor, and the comparative few who remained loyal to Terra were outliers. Many were of Terran origin or were those who had initially followed a legion master prior to finding their primarch, they were exceptions. When the same rebellion was attempted in the White Scars en mass and Jaghatai Khan remained loyal, it crumbled almost immediately upon his return. He was siding with the Emperor, and beyond those imprisoned, everyone else instantly fell into line without question.
The differences between the two events shows an ingrained loyalty to better warriors and concepts greater than themselves. Usually one which is an individual or more tangible form than anything else, perhaps exemplifying them as the pinnacle of some concept at the most. The point is that, once the leadership of such a group falls, many others would follow. The chapters were made to combat this, but in more ways than people often realise. Yes, splitting the legions did help to prevent this taking place and meant any defection would have only a small fraction of the impact it would have as a legion. At the same time though, the very training of each astartes' force was dramatically altered. A vastly greater emphasis was made upon the mental discipline of each warrior and, now aware of Chaos, the Codex's doctrines were formed to make them far more resistant to any influences. You can quickly see this just by comparing the way in which the Luna Wolves behave to the Grey Knights, Excoriators or even Ultramarines from M41. Yes, there is that same kinship and they retain the ability to occasionally crack a joke, but there is often far more steel to their words and behavior.
Such improved training led to obvious advantages in staving off corruption, and even the most extreme of their number stood a better chance of avoiding succumbing to Chaos. While exceptions did still exist and individuals, companies, or even chapters would turn to Chaos, they were not so easily done. There was no universal turning of their forces and Chaos was having to work that much harder to actually corrupt them. The largest scale examples of a massed turning were the Badab War and Abyssal Crusades, both of which offered Chaos nowhere near the number of traitors they had gained in the Heresy. Between fighting and the astartes becoming splintered into vastly smaller groups, there were far more targets to focus upon. It was far more difficult for them to again gain the power they needed to begin full scale civil wars. Even atop this however, the greater resistance so often meant that chapters would frequently retain much larger loyalist groups than found in the traitor legions upon turning. Following any civil war or attempt to turn traitor, a chapter's numbers would prove to be extremely diminished, often with only a few hundred joining Chaos once the smoke had cleared.
The actual split of the chapters themselves though, this had a distinctly unique advantage the legions had never possessed. Many have often commented upon the size of each force the legions wielded or the numbers, but rarely it seems does anyone actually consider how they operated. The legions were crusaders, and while that might seem like an obvious comment think about what it entails. The role is one of a military constantly on the offensive, constantly attacking others and launching forays to conquer new territory. They did this, but they rarely seemed to truly pull back to help properly defend locations or actually defend the Imperium itself. They were mobile battle groups used to constantly being on the move, constantly attacking others and taking new worlds, but so often they lacked the ability to hold a world and prevent it falling. So often that role of defence was deemed one without glory, without any opportunity to earn true recognition for their skills. Even after turning traitor this could be seen among some of them, with Angel Exterminatus suggesting the Emperor's Children allowed a major fortress to fall just so they wouldn't be tied down to it. This left only the the Iron Warriors and Imperial Fists trying to cover this ground, sometimes so thin that single squads were expected to garrison entire worlds.
The chapters were offered a way to overcome the innate defensive failing of of the legions in a stroke of true genius. Of all the worlds in the galaxy, the legions were often only closely tied to their homes. If Deliverance, Medusa or Barbarus fell under attack, the legions would turn and fight there thanks to it being their homes, where they were recruited. Splitting up the chapters allowed for that same connection to be spread across the adeptus astartes, with the newfound chapters having a thousand new homeworlds to recruit from. A thousand new worlds which the space marines would garrison, defend to the last man and help to serve as strongholds for the new Imperium. More importantly, they were able to fulfill more roles than just the average garrison would. The legions had used garrisons as just that, locations where small bands of astartes were intended to hold, remain and call for help if needed. By comparison chapter homeworlds were recruiting grounds, supply bases and normally massive fortresses. As such, while they lacked the legions' numbers and massed firepower, they were more self-sufficient and better spread throughout the galaxy. Rather than twenty groups moving here or there, the Imperium suddenly had a thousand who were far better distributed throughout its territories.
The actual subject of recruitment and numbers is often brought up when criticising space marine chapters. The formations are often brought up as far more limiting and sapped each force of their major strengths, but compare that to how the legions operated. Often each and every one of these hundred thousand astartes armies were only recruiting from a single world. While there were exceptions such as the Iron Hands, Imperial Fists and Ultramarines, the likes of the Raven Guard, Death Guard or Emperor's Children were very limited. They had number yes, but with only a single world to support that, losses to these massive units were far harder to replace. The Raven Guard in particular were noted to have trouble doing so, relying often all too heavily upon their Terran born warriors due to Deliverance's low population. The Death Guard were the same to a degree, and Mortarion's stringent insistence upon using only his homeworld as a recruiting ground was often a big limiting factor. To put it bluntly, all too often the legions' seemed to have difficulties sustaining their massive sizes and recovering from heavy casualties, even without the Codex's more stringent testing.
Following an event so costly as the Horus Heresy, it's hard to see how they could have survived while sticking to that same structure. Following the Scouring, the Imperium desperately needed to rebuild and consolidate its defences as fast as possible. The hammer-blow had been struck, the traitors forced back and the Imperium was stable, but it was still in critical condition. It needed more widespread astartes to help defend its territories and fast, and as such the more recruitment worlds now home to chapters helped to ensure its survival. What's more is that, by helping secure entire systems and having a strong space marine presence, certain worlds were far less likely to be attacked or to have their best warriors respond quicker. By breaking them down into companies capable of more proportional responses than the thousand or ten thousand man detachments of other legions, they could more actively move out to behead smaller threats as they arose. They would not be as prepared to face the massed assaults of the Tyranid Hive Fleets ten thousand years later; yet this meant the Imperium was not about to die to a thousand cuts by forces to small for the vast legions to respond quickly to. Or threats on that scale simply too dangerous to be taken down by the Imperial Guard.
None of these points citing the useful nature of chapter homeworlds are to say that having chapters tied to certain worlds was exclusively important. While it was fulfilling a role which the Imperium had previously been severely lacking, there was no insistence within the codex that all chapters would universally follow this rule. After all, many chapters would go centuries or even thousands of years without finding a homeworld and remaining fleet based. The Crimson Fists for one remained with their vessels for an extraordinarily amount of time prior to finding Rynn's World, and became fleet based again afterwards. The adeptus astartes on the whole retained the ability to host crusading companies as and when needed, even with an entire founding devoted to creating more, so they ultimately lost none of their previous capabilities. If anything this allowed the astartes to be afforded far more flexibility and diversity among their numbers, as with new homeworlds or chapters came new views and approaches to war. While they might have originated with the same chapter, the likes of the Mortifactors and White Consuls could not be more different from one another. As such, the ways of war and flexibility of the astartes as a whole only increased over time.
Sticking with the point of some astartes being crusaders though, the obvious point of their smaller size does still need to be brought up. It was still rare for any chapter to operate en mass, so even these crusaders were all too often numbering only one or two hundred at the most, with some exceptions such as the Black Templars. However, as a whole this still served a certain purpose within the Codex. The space marines were still relatively self sufficient and retained a degree of autonomy, yet at the same time they lacked the full firepower of a legion. This meant that they weren't so great a bunch of loose cannons as before and to spend more time relying upon the other Imperial military force for support. While they could certainly run in and enter battles, the astartes were more limited to being shock troops and would need Imperial Guard units to help hold ground or back them up. With them only technically being under the direct command of any space marine commander, and other Imperial units capable of counter-commanding their orders, it again prevented the same seen during the Horus Heresy.
Ultimately, the astartes did hold significant power and still had a great deal of firepower they could bring to bear. Unlike before however, they were now serving as a cog within a much bigger machine, rather than running ahead and expecting everyone else to keep up with them.
What's especially odd and sadly all too often overlooked is the degree to which the Codex Astartes allowed chapters to deviate from it as and when needed. To quote Captain Titus, how they "live with those rules is the true test of a space marine." That they can still be interpreted in more than just a narrow view and do allow leeway, even in basic chapter structure. The last article did mention Graham McNeill's works as something of a problem, namely in how his books all too often showed the Codex as being a hindrance without enough benefits. This said, his words about always trying to find a balance between when and when not to follow it are remarkably true, as even in the beginning many chapters were seen to broadly follow it and retain their own ways. Many deviated from it to a fair degree, with the Iron Hands, White Scars, Blood Angels and Salamanders all following a different structure thanks to requirement or choice. While the core of that same structure Guilliman laid out could still be seen in them, he never went so far as to try and stamp out any effort to follow their own set of laws.
Guilliman himself was not quite so narrow minded as many critics of the Codex Astartes seem to think. Quite often when looking at the first founding chapters you can find examples of that. Ignoring the above ones for starters, other early chapters were still permitted to deviate from it in one way or another, or outright ignore it. Of the two most famous examples, the Black Templars and Space Wolves, one was allowed thanks to a loophole while the other's differences were accepted thanks to a very different way of war, but still retained a mutual respect. In part, and this is just personal opinion, this could most likely be put down to the Codex itself not being solely Guilliman's work. One detail sadly all too often forgotten by critics and supporters alike was that the Codex incorporated the teachings and ideas of many of the primarchs, and to call it "Guilliman's book" is misnomer. That same encouragement for diversity and to retain an army's strengths over total uniformity we've already mentioned is still present here.
Atop of having certain chapters retain the ways of war which still made them unique, Guilliman himself made no effort to force any total breakup between his legion or others. While the Ultramarines themselves had increasingly distant connections with some of their successors, they still maintained close ties with others. Others among the legions were the same. Dorn went to great lengths to ensure that while no longer under the same banner, his scions would still have a strong sense of unity, and the Dark Angels had a similar co-ordination. Albeit their one was formed out of less pure reasons and more out of shame.
The point is though, that while Guilliman did split up their legions, he never wanted them to be entirely separate or cut off from one another. He and the others all understood a sense of brotherhood was still needed to ensure loyalty to one another and help prevent another major civil war. As such, while rivalries and conflicts would still exist among chapters, there was going to be enough there to help prevent any true sense of isolation.
The final point truly worth mentioning however, is that Guilliman's plan surrounding the chapters seemed to be ultimately unfinished. Struck down in battle by Fulgim, the astartes lost the major brain and political drive behind ensuring that the chapters continued to multiply in number or retain power. From what we can tell, the primarch's overall scheme seemed to involve continuing to increase each chapter's numbers and giving them further domains. While they would each control only a small semi-self sufficient sector of space, it would be the equivalent of the Imperium being split up into a thousand or so systems similar to Ultramar. Each able to govern its own needs, defend itself and remain individual while still ultimately answering to the bureaucracy of Terra. This would have solved many problems such as the long range communication issues, and allowed for faster responses, defensive efforts and maintaining the Imperium as a whole. You can actually see how the plan starts to fail as foundings produce less chapters and become a less frequent event over thousands of years.
Comparing the strengths and failings of each legions makes it hard to really comment which would be the truly superior approach to war. Both do have obvious strengths and failings, and it's not hard to see why some claim that the legions might have done a better job than the chapters in some cases. At the same time however, given what we know, it's still questionable as to how well the legions would have truly stood up when it came to protecting an established empire. That's really the crux of the problem here, comes down to the fact each faced down very different threats. The chapters were there to hold together a shattered galaxy and dig in to defend humanity, while the legions rescued vast swathes of worlds and completely annihilated xenos threats.
Really, the simplest way to settle this argument is just by focusing primarily upon the state of the galaxy when they were formed and compare it to the end of M41. With massive threats unlike anything the Imperium has seen before, it is fairly evident that humanity once again needs something on the scale of the legions to hold off the Tyranid Hive Fleets or counter the growing Necron threat. Both are simply too massive for the chapters to counter and the combined numbers and firepower of a full legion would allow for more decisive victories against them. At least victories without resorting to the scorched earth tactics it is currently having to employ. At the same time though, while this might be the case then, it's hard not to argue that the Imperium would not have reached that point without the chapters. The legions simply weren't suited to dealing with more minor threats or holding most of a galaxy together, and it would have likely been a far less stable empire without them.