The Night of a Thousand Rebellions was an insurrection against Imperial authority begun in 992.999.M41 that swept across large portions of the Segmentum Pacificus and was instigated by the forces of Chaos.
Carefully seeded rebellions sown across the Segmentum Pacificus all bore their bloody fruit upon the same night. Uprisings and discord struck at the heart of hundreds of Imperial worlds, including the supposedly secure Imperial strongholds of Enceladus, Darkhold and Minisotira.
Even the homeworld of the Lions Defiant Chapter was lost to anarchy caused by secret cults and frenetic agitators. Contact was interrupted with large swathes of the Segmentum as the Heretic Astartes moved in, revealing themselves as the orchestrators of the insurrection. They took advantage of the discord and disorder that reigned across the Segmentum to cement their control over as many worlds as fell under their assault.
- Codex: Chaos Space Marines (6th Edition), "The Long War," pg. 25
- Warhammer 40,000: Rulebook (6th Edition), "Age of the Imperium - The Time of Ending," pg. 177