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human
[Warhammer 40K]Does the Codex Astartes fundmentally weaken the Imperium?

It seems to me, from my readings on the Great Crusade that the Legiones Astartes under the Legion organization is nigh unstoppable. Nowadays it's wiped out there, completely destroyed over here, across the galaxy whole companies are wiped under the Codex. So is there a fundmental flaw in the Codex?
gpt
Both yes and no... Individual Chapters are sorely weakened from their days during the Crusade. No Chapter could hope to stand against, or emulate, a Legion. 

At the same time, it was the almost unfathomable strength of the Legions (remember, at the time the Imperial Army was subservient to the Space Marine Legions) is what led to the Heresy. The ability to turn that much military might against the governing body, so easily, was a serious risk to the continued stability of the Imperium.

By crontrast, look at Huron Blackheart. He convinced a dozen chapters to side with him, swaying more commanding minds than Horus did (he only had to convince 7 people) and he was only able to garner a fraction of the strength of a single Legion. 

It's one of those weird things, that the Codex Astartes both strengthened, AND weakened the Imperium... It diminished their overall military strength, though it made it considerably more stable.