Editing First Founding (section)

== Horus Heresy ==

{{Main|Horus Heresy}}

For all their power, the [[Space Marines]] and [[Primarchs]] were not perfect; ([[Alpharius|may]][[Omegon|be]]) half of them were sufficiently flawed to be tempted by (or driven to) [[Chaos]], led by Warmaster [[Horus]]. The traitors were defeated, but at a terrible cost, including the near-death of the [[God-Emperor of Mankind]] and trillions of deaths of invaluable astartes and human beans.

[[Roboute Guilliman]] decided that the so-called [[Horus Heresy]] was proof that one man could not be trusted with power over one-twentieth of the Imperial Armed Forces, so he enacted several reforms to divide the Imperial Army into the Imperial Guard and Navy, and split the remaining loyalist Legions into Chapters, in accordance with his [[Codex Astartes]]. This event was later known as the [[Second Founding]].