Be warned, there are quite a few Spoilers here. But considering Brotherhood of the Storm was a collector's edition book (and excellent), there's only 5764 copies of the book out there (and you can't have mine!). So you may want to continue reading all the same.
(Spoilers starting here)
Some basick backgruond for the book. The Novella presents this brief story about the White Scars from three points of view. That of Targutai Yesugei, a Stormseer. Shiban Khan, Khan of the Brotherhood of the Storm. And General Ilya Ravallion, of the Departmento Munitorium. The accounts take place during three different time periods, dependant on the character. In General Ilya's story, we see the senior but tiring officer sent to post-triumph Illanor to seek an audience with the Khan, who is known to be elusive and want to roam by his very nature, in the hopes of resolving certain logistical issues caused by their doctrines. Though first she must track down one of the Stormseers, Targutai, who serve as Jhagatai Khan's personal emmisaries and messangers. Through her we see how they relate to ordinary humans, their Crusade auxiliary forces, and the Imperium in general, which is unintentionally distant. Her straightforward honesty, and open mindedness manages to impress the Asartes and their Khan, and she becomes their permanent liasion, at least as late as the begining of the Horus Heresy. Shiban Khan's story takes place during that time, though it is told in such a style and tone as to indicate that the author is penning it after the Heresy has ended. It discusses the war on a planet called Chondax, where the Legion as a whole is wiping out the last remnants of the Ork empire that was shattered at Ullanor, a task it has been pursueing in whole or part for some time. We learn that though the Legion stayed loyal, Horus had good reason to believe that they would side with him during his revolt, as at least one Company (Minghan/Brotherhood) of 500 had been turned to his cause, after being seconded to his Crusade Fleet. After spending the culmination of the campaign working together, the two Khan's clash in personality somewhat (one Terran, the other Chogoran), but ultimately accept each other as brothers. The story never makes it clear whether the Legion comes to blows with itself, or those who had been swayed by Horus will cast off his influence and ride with their Legion and Primarch. Near the end of Shiban Khan's story, we see Jhagatai Khan apparently being informed of his brother's treachery.
Targutai Yesugei's story is the one most relevant to my point, though is also the one more distanced from the 'current' timeline of the Horus Heresy series. It takes place during his childhood on Chogoris, before his Primarch is even found by the Emperor (indeed just as he is begining to unite all of the tribes). In the story the young psyker is singled out because of his golden eyes and as a test is sent up an ancient mountain along to make contact with the gods. Staring out accross the endless plains he has a vision, of Imperial warships bearing the insignia of the Legions (including "the lightning strike in gold and red, the eternal mark of the Khans") smashing each other to pieces in brutal combat, and then another one. There, four figures representative of the Chaos Gods stand on one side, wordlessly ordering him to drink from a cup filled with blood and power. From the other side a figure of pure cold light is walking toward him, but never growing closer. He decides to take only one sip, to be courteous, thereby dissapointing them all with his choice. But perhaps the golden figure less. To briefly finish off the story, Targutai's powers awaken and the following morning he goes to rejoin the escort his khan had sent with him, only to find they had been murdered by the 'Khitan' (the people of the Palatine), fleeing from them, and eventually ending up in the hands of The Khan, who shared with him some of his vision and philosophy, accepting him as a zadjin arga of his household, and is marked with the lightning bolt scar beneath his left eye, as is tradition with the Talskar people (herbal dyes make the scar white).
While that was quite a long tangent, I only wanted to share a bit of a wonderful story, hoping you all enjoy 40K lore as much as I do. And getting on with things, if one were to consider Targutai's story to be a metaphor for, if not the people of Chogoris as a whole, then perhaps the Legion, looking at the account given within the novella and the description of their Primarch's Curse some interesting correlations arrise. While I paraphrase, what we are presented with in First Founding is the idea that if a White Scar 'drinks too deeply' of the dark and savage power inside of him, he can be lost to it forever, nothing more than a beast and a monster to be chained up. In essence, they might be said to have taken a 'taste' of Chaos, but most never go any further. But as with all things of the warp, a taste all that's needed to doom yourself, if the other circumstances are right. Hence the Curse and its effects. And yes, I'm quite aware that Corruption is tied to something entirely different than the Primarch's Curse, but I'm trying to look at things from a more abstract angle, as that can be necessary when one is trying to fit fluff to rules.