Editing Nobledark Imperium Imperial Forces (section)

===The Breaking of the Legions===

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During the Great Crusade the Adeptus Astartes were organized into twenty distinct legions, each composed of thousands of Space Marines. By M41, however, the Adeptus Astartes have been divided into many distinct chapters, each about 1000-1200 strong and each descended at least in part from one of the eighteen legions that survived the War of the Beast. The reasons for this change in organization are complicated; many lay students of history often claim that the impetus for this change was Roboute Guilliman's Codex Astartes, published in 243.M31. However, like much of Guilliman's work, the Codex Astartes was meant to be a thought exercise in how the Adeptus Astartes could be more efficiently organized in a post-Great Crusade environment, and Guilliman would never have tried to shove his ideas down his fellow primarch's throats.

In truth, all of the legions split up for different reasons, and at different times.

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Several of the legions survived virtually intact for a little while longer under their new leaders, who would have probably been considered primarchs in their own right if they hadn't had to stand in their predecessors' shadows. Kharn found himself essentially taking over more and more of his legion's duties as Angron's health deteriorated. Abbadon was ambitious and charismatic enough to keep the Void Wolves in one piece for at least another generation. Leman Russ told Bjorn during a moment of mutual drunkenness to "look after the place while I step out for a minute". The next morning they realized Russ was gone and to make matters worse everyone had been just sober enough to remember what Russ had said the night before.

Other legions split up following the death of their primarch, or for simple matters of practicality. Old Man Khan called a meeting of the yabgu, despite not being dead yet, to make sure that whoever succeeded him would be competent enough not to run the legion into the ground. In a rare moment of humility, the yabgu compared themselves to Khan and realized that none of them could claim to have accomplished what Khan had accomplished by their age, and so the legion was split up. The descendants of the Thousand Sons, such as the Grey Knights, were already split up before their primarch's death (with the exception of the Blood Ravens), given that all were created to perform quite different, specialized tasks. The Imperial Fists found themselves splitting apart to fortify and garrison agri-worlds after the War of the Beast, on the basis that one cannot rebuild an empire if everyone is starving, and gradually drifted apart over the centuries. The same is true of the Iron Warriors and hive worlds and Iron Hands and forgeworlds. In these cases, Guilliman's Codex Astartes was seen as a natural framework for how to rework the legions into more autonomous units (though each legion implemented the Codex in their own way).

The Dark Angels are rather infamous for having split up before Guilliman ever wrote the Codex Astartes, after two-thirds of their number turned traitor during the War of the Beast. The Lion split the remaining loyalists into knightly orders and instituted the rank of Watcher to ensure that no one individual could ever subvert the entire legion. Guilliman may have actually been thinking of the Dark Angels when he wrote some parts of the Codex.

The Death Guard never really split up, even with the death of their primarch. Unlike the other legions, they have never truly stopped marching to war.

There were two real death knells for the concepts of a legion as a whole. The first was when Belarius the Abdicator refused to take up command of the full host of the Blood Angels after the death of Sanguinus, knowing full well that his entire reign would be spent in the shadow of the Martyr Angel. Instead, he took command of a much more reasonably sized contingent of Blood Angels, nearly all survivors of the War of the Beast, with Belarius giving the most competent of the remaining Blood Angels command of their own groups. This set the precedent for most legions of breaking up into chapters after the death of their Primarch.

The other was the “Iron Cage” incident that happened to Fulgrim sometime in early M31. Fulgrim had always been a micro-manager, and was one of the strongest opponents against breaking the legions into chapters. However, after the War of the Beast, the sheer number of small-scale conflicts across the rebuilding Imperium and a lack of local autonomy meant that the Empire’s Sons were ground down to about half the size of their prime merely by attrition alone, despite being one of the biggest recruiters of new Astartes. The breaking point for the legion was when the Empire’s Sons got caught in a trap set up by a Tzeentch-worshipping Big Wyrd. The Wyrdboy was never caught, and by the end of it Fulgrim was left with enough marines to scrape into a little less than three chapters. After that point, even the strongest detractors of the Codex Astartes (with the exception of some particularly stubborn cases like the Death Guard) had to admit that Guilliman had a point.

However, despite this, successor chapters have not completely caught all ties with one another. Most chapters still retain close ties with their former brethren in other chapters, and many chapters have officer exchange programs to encourage loyalty to the Imperium as a whole rather than a particular world or individual. Nevertheless, chapters are expected to be open about all inter-chapter interactions, and unofficial brotherhoods are officially banned by explicit decree of the Emperor to prevent the rise of another individual like Luther from fostering ties of soft power beneath the nose of the Imperium. One of the jobs of the Inquisition’s Ordo Militarum is to make sure the Adeptus Astartes keep to this decree.
 
Additionally, by his own admission, Guilliman’s organizational suggestions were designed for times of relative peace, rather than all-out galactic war. In times of great crisis, the First Founding chapters (who are considered first among equals among successor chapters, and whose original members were often some of the best soldiers of each legion) have the right to call for a Reformation of the Legion, where the successor chapters would temporarily unite to lock arms and march under the united banner of the old legion once more. This policy is sometimes called the Last Wall policy, as Guilliman reputedly got this idea based on suggestions by the consummate soldier Rogal Dorn, who understood that the War of the Beast was not going to be the last major war the Imperium would face.
 
Responding to this call is completely voluntary, but many chapters consider it shameful for a successor chapter to refuse to answer the call, particularly since a call for a Reformation of the Legion is reserved for only the direst of emergencies that threaten the entire Imperium. The only time a refusal of the call is ever considered acceptable is if a chapter is severely undermanned or if they are physically unable to respond due to being directly under attack themselves. For example, the Lamenters were unable to respond to a call for the temporary reformation of the Blood Angels during the 12th Black Crusade, due to suffering from severe manpower losses beforehand. The Lamenters still blame themselves for not being able to respond to the call, even if the rest of the Imperium doesn’t.

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