Atmaran War

The Atmaran War was an Imperial castigation campaign conducted against the world of Atma II by the Ordinators Space Marine Chapter, that had fallen into bloody insurrection. Unbeknownst to the Chapter, the true threat behind the secessionist movement was instigated by agents of the nefarious Alpha Legion Traitor Legion.

History
The Sector Capital of Atma attempts to lead a secessionist movement to break the planet away from the Imperium of Man under the guise of "reforging a new empire in the Emperor's true vision". Unknowingly to the inhabitants of the world of Atma II, the rebellion is lead by a pawn of the traitorous Alpha Legion. Intuiting the role of the Dark Gods, the Ordinators and eleven Imperial Guard regiments engage in a war to surgically cut out the corruption from the massively populated sector to spare the lives of as many as possible, though most of Atma II itself is purged in the process. The war ends with the killing of the Chaos Lord Ukon in a hidden bunker at the core of the world, followed by the seizing and public execution of the rebellions' leader on live holo-vision. The remaining population of Atma II - approximately 41% of the pre-war citizenry - are ultimately spared only because the preaching of the chapter's Reclusiarch guides the better part of the native PDF forces to redeem themselves and to seek forgiveness through death in battle against their treacherous brethren.