It is the 51st Millennium, and the galaxy has been still.
The Imperium has been long dead after the cataclysm of the 42nd Millennium. Though few remain that saw the end with their own eyes, myths and legends state that the heroes returned, gods were born and slain, the ancient metallic horrors from beneath the surface rose, the Orks fought so hard and so constant they became nigh-extinct for ten thousand years, and the Aeldari finally died.
The Chaos Gods reduced to null, the Rift closed. The Traitor Legions found themselves cut off from their patrons, with many no longer blind to their heresies. The daemons of old became the stuff of bogymen and stories before bed.
The great tide of Tyranids were somehow quelled, this feat unknown save but tales of old men, which we will get to later.
But the close of the 42nd Millennium was not without loss. The Emperor, for one, finally allowed to rest after saving his people one last time. Terra, not destroyed but cut off without supplies or resources. Communication became rare, the Astropath Houses of the old Imperium reduced to but a dozen from the sheer casualties during the Final Wars of the age of the Imperium.
There is no unifying force in the Galaxy anymore. The Lost and the Damned have no gods, Humanity has no Emperor, the wild Tyranids no hivemind, the feral Orks no major Warbosses, and the Necrons have no Silent King. The Tau have no Ethereals, and the remaining Adeptus Astartes have no Primarch.
Across the galaxy there exists small pockets of civilization. A hundred thousand Imperiums, empires, dynasties, and kingdoms. A few worlds have the luck of having a strong military, others don't. While the galaxy is still, it is not calm. War is not gone, for border conflicts and resource wars occur commonly. Understanding is not here, for the cruel fates experienced in the Age of Strife, Age of the Imperium, and the Age After have created grudges that may never dissipate.
It is the 51st Millennium, and the galaxy is awakening...
Part One - The Godless Legions and their Patronage
With the end of the Imperium came the near-end of Chaos. While to truly kill Chaos anything with a soul or mind must be killed as well, the Gods of Chaos and their heretical warriors were decimated by the apocalyptical conclusion of the Age of the Imperium. Be it the Emperor, the Aeldari God of Death, the survivors of their Pantheon, something else or all of the previously stated, it is truth the Gods have reduced to null.
The Heretic Astartes and the various and unending cults of Chaos found themselves in a strange predicament as well. Either continue their worship with few benefits if any at all, or abandon their former masters. Without the grasp of Chaos blinding those who worship them to the horrors they have wrought and the travesties they are, most chose to abandon the dead gods for better lives.
Few leaders of Chaos survived Abbadon's Final Ploy. It is known that during the march on the Throne Room, Abbadon himself was slain by a hero of the Imperium and final defender of the Emperor, who was too busy fighting off the Gods at their height to interact with the Physical Realm, lest he lost. Legend disputes whether this was the heroic act of Roboute Guilliman, Lion El Johnson, one of the Custodians, Rogal Dorn, or one of his Damned Legionnaires. But one of the most beloved theories, despite its unlikelihood, is that he was overwhelmed by nearly a thousand Guardsmen; a literal wave of bodies and las-shots to drown the Warmaster of Chaos Undivided.
Whomever claimed the long fallen Astartes, it is known that he in fact did die that day. One by one the Daemon Primarchs fell soon after, either by their patron unable to sustain them constantly any longer or being bested by their Loyalist brothers without a god to crawl back to in the Warp. One did survive, however, but these specifics have been lost to time.
With no gods to worship, the skull throne trampled, the garden burnt to the ground, and the Palace of Pleasure detonated with the force of a million suns, what remained of the Legions disbanded. Some tried to take advantage of the destroyed galaxy, and a few did manage to build their fiefdoms out on the edge of the galaxy. These 'Chaos Kingdoms' typically worship the skeletal Chaos Gods, and their dead but still powerful corpses give their worshippers slight power, without the control of the Gods over them.
The five Great Chaos Empires are the Cthonian Kingdom, the Bile Trade Empire, the Guard Kingdom, the Magnian Fiefdom, and Huron's Phoenix Imperialis.
The Cthonian Kingdom is made up of primarily former Black Legion. Based in the few remaining chunks of their homeworld, the Cthonian Kingdom is likely the second weakest Great Empire. While it may have nearly four thousand Black Legionnaires, along with nearly a billion mortal troops and nearly a hundred warships, they have constant squabbles and their leaders come and go in a matter of decades, centuries if they're particularly crafty. They are also engaged in constant war with the Reformed and the Ultramar Empire, who we will get to later.
The Bile Trade Empire is the network of the Spyder made a lot more literal. With the Legions all but gone, he found many desperate warlords rushing to him for resources. Using a stolen Strike Cruiser's resources and equipment as the springboard for his new enterprise, he forged a massive feudal kingdom through trade, bartering, and resource collecting. He even created a new currency named legumes, however this is contraband in most 'loyalist' territories as it signifies trading with the overall distasteful Chaos empires. While Bile himself has abandoned Chaos for they no longer serve his purposes as they are corpses, many within his empire still believe in the Fallen Gods and thus it is generally counted as a Chaos Empire, however it is unique in the regard of not being completely devout.
The Guard Kingdom is an odd one. While having the strongest navy of the Chaos Kingdoms, it in fact has a single Astartes; its leader. Simply known as the Guardian, he is the last of the Traitor Legion of the Death Guard. The rest too putrid to live past their God's death, the Guardian somehow avoided the fall of the Death Guard originally and kept going uncorrupted, despite his Legion's fate. Posing as a Word Bearer for nearly ten thousand years, after the death of Lorgar and the fall of Chaos the last Death Guard decided to build a small little town on the edge of the galaxy. However, by defending his town from feral Tyranids and feral Orks, many came to follow him. Due to his unwavering belief in Chaos, this became the state religion and soon a Chaos Kingdom was born as his solar system was united in fifty years. Soon, one system became two, and two became four, until he had become a nation of five hundred vessels, six hundred million soldiers, and eighty-five worlds.
However, the Guard Kingdom have found themselves waging war against both Imperial Remnants and the new Major Xenos Empires. They remain bulwark, for now.
The Magnian Fiefdom is a tale of tragedy and victory. As Chaos crumbled at the end of the Forty-Second Millennium, the Thousand Sons were broken. With but twenty-five Sorcerers left, they united at the now-shattered Planet of the Sorcerers, Primarchless. Licking their wounds, they managed to defend themselves from the remaining Drukari kabals, Chaos raiders seeking to capture the Sorcerers and use their psychic powers to fuel their rituals, and some of the remaining Imperials who wanted but retribution for the death of their Emperor.
With fifteen Sorcerers left but managing to rest and rebuild their psychic strength without relying on a god, the remaining Thousand Sons were too tired to continue until they found a single feather of Magnus the Red, deep within the halls of the labyrinthine world. Using it in a final ritual, the world was hidden from view and the fifteen Sorcerers finally had a change to recouperate.
Forming the Council of the Fifteen, the Sorcerers debated what to do next. While fourteen of the Sorcerers decided to slowly grow their ranks by searching for psykers across the galaxy and teach them in the ways of the Warp, the fifteenth decided against it and wished to leave for the Cthonian Kingdom, wishing to continue the fight. Not about to risk giving away their position to the mad sons of Horus Lupercal, The now Council of the Fourteen captured him and sacrificed the traitorous sorcerer to the Feather of Magnus, keeping it charged despite constant use.
From there, they began their search for new psykers and their ranks grew quite quickly, gaining plenty of human psykers, Tau psykers (to which we will discuss shortly), captured Zoanthropes from the feral Tyranids (a rare species, considering the psychic backlash of the death of the Hivemind), and even a single Aeldari farseer, who sees potential in the Psyker Empire but is wary of it should it turn on its original ideals of showing the galaxy the worth of Psykers, or should it take that goal to a violent end.
Recently, they've begun experimenting in attempting to fix the dead Rubric Marines and restore them to fighting shape.
The Phoenix Imperialis is a horrifying portion of the galaxy. Led by Lucius, the former eternal Space Marine who barely survived after the death of Slaanesh through determination and fear of death, and Huron Blackheart, who manipulates all within his realm, including Lucius. Even though Slaanesh was the first god to die, his corpse remained rife with power. Huron met Lucius, who at this point was a brutalized Astartes on a pike, slain by the unleashed souls of the heroes and champions who were consumed by him for feeling pleasure for killing him. No longer the Eternal, Huron saved him and managed to use his apothecaries and healers to piece him back together. Humiliated, Lucius fights harder than even his former self in the Heresy or Great Crusade in an effort to restore his honor and pride.
The bulk of Huron's Phoenix Imperialis, and the reason why its called such a thing, is due to the remnants of the Emperor's Children mostly coming to him. Be it fate, coincidence, or something else, Huron was met by nearly a dozen Emperor's Children vessels and two thousand Astartes, along with tens of thousands of cultists. Managing to manipulate their leader, the Emperor's Children and Cultists joined his tri-world empire, and the combined forces of the battered Red Corsairs and Emperor's Children expanded his realm by nearly forty systems. Due to the vast majority of his forces being the harlot armies of Slaanesh, the conquered people of his empire inevitably followed suite in their Astartes Lords' beliefs. The Empire worships Fulgrim along with Slaanesh, believing his return will herald upon the New Age of Chaos because of the promise he made before the Second Siege of Terra, that being once the Emperor is slain that Chaos will finally win the Long War and the galaxy will be theirs. This promise obviously unfulfilled, many do believe he will return. However, a conflicting story, one told by the fragmented and long shattered Imperials, is that Fulgrim died in combat with his loyalist counterpart and a flame-wrethed Dreadnaught...
The Chaos Legions not mentioned already are the Word Bearers, World Eaters, Alpha Legion, Night Lords, and Iron Warriors. Their fates are a lot different than the other Legions, namely because they are much less unified save the Word Bearers, and the World Eaters almost followed suite with the Death Guard.
The Night Lords shattered apart and many went onto create their own fiefdoms of terror. Already Primarchless, they were essentially without leader before, and finally given the chance of separation, they did so and strived in this new galaxy, unfortunately never seeming to rise to the height of their brethren. Too much internal squabble, and its not uncommon to see one Night Realm fight another.
The Iron Warriors' realms were different. There were less of Iron Warriors pocket empires than any other legion; however, they were well defended. Most Imperiums and other empires dreaded fighting an Iron Realm for they knew each campaign launched was to be a meat grinder. These Iron Realms rarely expanded past their own borders though, however the Sons of Dorn or their descendants are known to hunt down these pocket empires with extreme prejudice.
The World Eaters, with Khorne finally dead and his grip released from them, were stripped of their rage, calming down for the first time in ten thousand years. While the World Eaters always struggled with their rage, now they were weakened and calm, never to rage again. Reduced to the strength of but a barely augmented scout, the tired Eaters disbanded. Most went off to live better lives in the Imperial Remnants. Most upon arrival were shot and killed for their heresies, but some were merely welcomed. They helped with local projects and lived normal lives, and a few who weren't too scarred by war helped to train PDF.
The Word Bearers legion is much different. Lorgar's final order to his legion were to investigate the Gods' supposed death. Unable to believe his pathetic corpse of a father befell the greatest beings in the universe, he sent all of his forces into the Eye of Terror even as his personal warship detonated, with him onboard. The infamous collection of warp storms closed soon after they entered the Warp, and the Word Bearers have not been seen since, besides the few warbands who cleaved small realms for themselves or joined the Cthonian Kingdom.