30k

30k is a common shorthand for the fictional setting of Warhammer 40,000 during the Horus Heresy era. This period, approximately 10,000 years before the main Warhammer 40,000 timeline, depicts the galaxy-spanning civil war that saw the Imperium of Man fracture. The term "30k" derives from the year 30,000 of the Imperial calendar, which marks the height of this conflict.

The Horus Heresy was initiated by the Emperor of Mankind's eldest and most favored son, the Primarch Horus Lupercal, who was corrupted by Chaos. This betrayal led to half of the Emperor's genetically engineered sons, the Primarchs, and their respective Space Marine Legions turning against the Imperium. The conflict resulted in immense destruction, the death of billions, and fundamentally reshaped the Imperium into the grim, xenophobic, and theocratic entity seen in the Warhammer 40,000 setting.

The 30k era is characterized by a more hopeful, albeit still harsh, Imperium under the direct leadership of the Emperor and his Primarchs. Technology was more advanced and widely distributed, and the Emperor's vision for humanity's future was still a tangible goal. The Horus Heresy represents the tragic fall from this nascent golden age into the darkness that defines the later millennia. This setting is primarily explored through the Horus Heresy novel series and associated games published by Forge World.