Exterminatus is the sanctioned annihilation of an entire world, invoked when its continued existence is judged a greater threat than its loss. It is the ultimate expression of a doctrine that values the survival of humanity above any single population, holding that a planet too corrupted, infested, or compromised to save must instead be scoured of all life.
The order is not given lightly, for it destroys not only enemies but the world's people, resources, and future. Authority to enact it rests with a small number of extraordinarily powerful figures whose remit is the defence of the species against existential dangers. Justifications include unstoppable alien infestation, a breach between reality and the Warp that cannot be sealed, planetary rebellion allied to dark powers, or the presence of knowledge so dangerous it must never spread.
The methods vary in scale and cruelty. Some techniques sterilise the surface with firestorms or bombardment, leaving the crust intact; others employ engineered plagues, atmosphere-igniting weapons, or devices capable of cracking the planet apart entirely. Whatever the means, the intended result is the same: a lifeless husk where a living world once turned. Those who order it regard the act as a grim mercy and a necessary duty, while its survivors, when any remain, remember it as one of the most terrible powers ever wielded in the name of survival.