The 40K timeline
From the War in Heaven 60 million years ago to the Era Indomitus. Dates use the Imperial calendar (M = millennium).
The War in Heaven
The Old Ones, first space-faring race, war against the Necrontyr and their newly-discovered C'tan Star Gods. The Old Ones bio-engineer psychic warrior races (Aeldari, Krork/Orks, Mankind) to fight the C'tan, while the Deceiver tricks the Necrontyr into biotransference, birthing the soulless Necrons.
Necron Revolt and the Great Sleep
The Silent King Szarekh shatters the C'tan into thousands of enslaved shards after they betray and devour Necrontyr souls. Too weakened to face the ascendant Aeldari, the Necrons retreat into stasis-tombs to sleep for sixty million years.
The Aeldari Empire at its Height
The Aeldari inherit the galaxy as the Empire of Ten Million Suns, mastering the Webway and handing all labour to constructs. Freed from purpose, the immortal hyper-sensual race slides into decadence and pleasure cults over millennia.
Humanity's Golden Age
Mankind's interstellar utopia rests on the Warp Drive, Gellar Field, Navigator gene, and the STC. Far more advanced than the modern Imperium, it ends when the AI Men of Iron rebel in the Cybernetic Revolt, leading to the permanent ban on Abominable Intelligence.
Old Night
Some 5,000 years of anarchy as Warp storms isolate every human world and proliferating psykers open daemonic incursions. Only worlds that ruthlessly suppressed psykers survived, seeding the Imperium's eternal psyker-hatred.
The Birth of Slaanesh
Aeldari decadence gestates a new god in the Warp; when Slaanesh is born it implodes psychically and devours trillions of Aeldari souls. The cataclysm tears open the Eye of Terror and, by clearing the Warp storms, enables humanity's Great Crusade.
The Emperor and the Great Crusade
After conquering Terra in the Unification Wars, the Emperor creates twenty Primarchs and their Space Marine Legions and launches a two-century campaign to reunite all human worlds under the secular Imperial Truth. He names Horus Warmaster and withdraws to Terra to pursue the secret Webway Project.
The Horus Heresy
Corrupted by Chaos via Erebus and a false vision, Warmaster Horus turns half the Legions against the Emperor in a galaxy-spanning civil war. Atrocities like Isstvan III, the Drop Site Massacre, and the Burning of Prospero mark the conflict's escalation.
The Siege of Terra
Horus besieges the Imperial Palace; Sanguinius is killed and the Emperor at last destroys Horus's soul but is left mortally wounded. His ruined body is interred on the Golden Throne, repurposed as life support, beginning his 10,000-year half-death.
The Codex Astartes and Second Founding
Guilliman authors the Codex Astartes to prevent another Horus, breaking the Legions into independent ~1,000-strong Chapters via the Second Founding. He himself is later mortally wounded by the Daemon Primarch Fulgrim and placed in stasis on Macragge for 10,000 years.
Rise of the Ecclesiarchy
Despite the Emperor outlawing his own worship, Emperor-worship becomes unstoppable and the Adeptus Ministorum is adopted as the state religion. The Imperium calcifies into an oppressive, heresy-obsessed theocracy that venerates rather than understands technology.
The War of the Beast
The largest Ork invasion in history, led by six Prime-Ork 'Beasts', threatens Terra and nearly annihilates the Imperial Fists. It is resolved by Sisters of Silence and the purge of the corrupt High Lords known as 'The Beheading'.
The Age of Apostasy
Goge Vandire seizes both the Administratum and Ecclesiarchy, unleashing the decades-long Reign of Blood. The Confederation of Light under Sebastian Thor resists, and Alicia Dominica beheads Vandire before the Golden Throne, leading to the founding of the all-female Adepta Sororitas.
The Necrons Awaken
The Silent King Szarekh ends his intergalactic exile after encountering the leading tendrils of the Tyranids, recognizing them as an existential threat. Tomb Worlds wake unevenly across late M41, many with catastrophic 'bad awakenings'.
The Tyrannic Wars
The extragalactic Tyranids arrive as the Great Devourer, consuming all biomass. Hive Fleet Behemoth is halted at the Battle of Macragge, Kraken devastates Iyanden, and the colossal Leviathan attacks from below the galactic plane.
The 13th Black Crusade and the Fall of Cadia
Abaddon the Despoiler launches his greatest Black Crusade and destroys the Fortress World of Cadia by ramming a Blackstone Fortress into it, shattering the Necron Pylons that held back the Eye of Terror. Only ~3 million survivors are evacuated through the Webway.
The Great Rift Opens
The Cicatrix Maledictum, a galaxy-spanning belt of Warp storms, tears across the galaxy and cleaves Imperial space into Imperium Sanctus and the cut-off Imperium Nihilus. The Noctis Aeterna blots out the Astronomican, and the opening of the Rift defines the boundary into M42.
The Return of Guilliman and the Indomitus Crusade
Roboute Guilliman is resurrected by Belisarius Cawl and the Ynnari's Yvraine, becoming Lord Commander of the Imperium, and Cawl reveals the new Primaris Space Marines. Guilliman launches the Indomitus Crusade, the largest mobilization since the Great Crusade, to reclaim a shattered Imperium.
The Lion Returns and the Pariah Nexus
Lion El'Jonson returns from a Warp-adjacent realm as 'Knight of Nihilus', saving the Blood Angels from the Daemon Primarch Angron. The Silent King advances the Pariah Nexus, vast null-fields meant to disrupt the Tyranid Hive Mind, while the Imperium fights on every front and barely survives.