The entire Imperium of Man was torn apart by a sudden large-scale rebellion.
With Horus dead, the expeditionary forces that had sworn loyalty to the Imperium immediately fell into chaos and loss of leadership.
The other loyal Primarchs, who lacked Horus's prestige, could not command their brothers or the Imperial armies and could only wait for Terra's decisions.
Malcador was shocked to learn that Horus had fallen in battle.
Yet he still continued to resist and ordered his subordinates to send messengers to the loyal Legions, demanding that they unite and suppress the traitors.
Lorgar, Fulgrim, Perturabo, and the other loyal Primarchs responded to Terra's orders and gathered.
Fleets appeared one after another from various star systems and assembled into a torrent of steel in the void.
Upon receiving Terra's orders, Guilliman immediately agreed to dispatch his armies.
His reply to Terra was full of respect and orderly, showing the usual strictness and loyalty of the Lord of Ultramar.
However, soon afterward Guilliman contacted the rebel leader Lion and held a long and dangerous conversation with him.
For the future of humanity and to avenge his adoptive father, Guilliman seized this opportunity and resolved to support the traitors in destroying the Imperium of Man.
After receiving Guilliman's promise, Lion and Sanguinius, together with the other traitor Primarchs, decided to reverse the situation and ambush the loyal Primarchs.
After careful consideration, they chose Ullanor as the battlefield.
Ullanor, the place where Horus had been appointed Warmaster, symbolized the turning point of the Great Crusade.
They chose this location also to tell the world that a new turning point was about to arrive.
Lion seemed the most pleased about choosing Ullanor.
He wanted to use the blood and defeat of the loyalists shed here to tell the world one thing.
He and Lion El'Jonson were the most powerful candidates for Warmaster.
It had been a terrible mistake for their father not to choose him.
The loyalist forces surrounding them were enormous. Warships filled the sky. With overwhelming power, they intended to thoroughly crush these detestable rebels.
Both armies clashed in a massive battle at Ullanor.
Fleets collided in the void. The light of cannons illuminated the entire cosmos.
Volleys of fire were like new stars being born in the darkness and then vanishing just as quickly.
Plasma beams traced silent, deadly arcs through the vacuum.
Torn warships burned in the void and slowly collapsed.
Giants clashed on the ground. Each step of their sacred machines shook the earth.
The volcano cannons of Warlord-class Titans bombarded mountains, shearing off the peaks in an instant.
Molten rock flowed down like red waterfalls, swallowing the infantry fighting below.
When the Marauder Titans launched their missiles all at once, thousands of white contrails crossed the sky, as if the fingers of the god of death were writing illegible names in the heavens.
As the loyalists and rebels fought fiercely, the number of casualties continued to rise.
The land of Ullanor was stained with blood in every corner. The air was filled with the stench of ozone, burnt flesh, and rust.
As the fighting between both sides intensified, the Ultramarines belatedly joined the battle.
Guilliman's army was the largest in scale, possessing an overwhelming fleet and more Titans than both armies combined.
At first, Lorgar and the other loyal Primarchs were extremely excited.
As long as Guilliman's Ultramarines were there, victory was certain.
However, the Ultramarines who joined the battle did not open fire on the rebels. Instead, they turned their attention toward the loyalists.
The first volley caught the royalists by surprise.
The fleet of the Emperor's son was the first to suffer damage. Numerous ships were engulfed in flames, their void shields penetrated, and blown to pieces.
Fulgrim's flagship, the Imperial Pride, became the target of concentrated fire.
The void shields were paralyzed by overwhelming firepower. Shells struck the ship, destroyed it, and it exploded in the void.
Seeing this, Lorgar's smile vanished. His expression changed from confusion to shock, and then from shock to rage.
"Guilliman, how dare you… how dare you do such a thing…!!"
The betrayal of the Ultramarines instantly reversed the tide of battle.
What followed was no longer a battle, but naked slaughter.
Fulgrim boarded Guilliman's ship, plotting to eliminate him and reverse the situation.
However, Guilliman had already foreseen this.
The Emperor's Children who boarded the ship were surrounded and attacked by the overwhelmingly numerous Ultramarines and suffered enormous damage.
Fulgrim himself was also seriously wounded in this battle, suffering severe damage from a Warp weapon that Guilliman had prepared in advance.
The Emperor's Children paid a great sacrifice to retrieve their Primarch. Otherwise, Fulgrim would have become the second loyal Primarch to be killed.
The loyalists were routed. Their armies collapsed like a castle built on sand.
The loyalist fleets fled toward the outer edges of the Ullanor system without putting up proper resistance, like a flock of sheep scattered by a wild beast, intending to jump into the Warp from there.
The ground battle was even fiercer. The Titan Legions and Space Marines loyal to the Imperium were surrounded.
Sacred machines were destroyed one after another by saturation attacks. The light from reactor explosions was clearly visible even from space.
The Space Marines loyal to the Imperium were surrounded by enemies several times their number and, no matter how hard they resisted, were slaughtered.
This battle became known as the Ullanor Massacre.
With this single battle, the Imperium's loyalists were severely weakened.
The news caused a great shock, and even more people throughout the galaxy chose to betray the cause.
Guilliman and the other rebel Primarchs seized this opportunity to announce the formation of the Human Federation.
Sanguinius, with his angelic appearance, took office as the President of the Federation, with its headquarters in the Baal Star System.
His inauguration speech spread at astonishing speed to every corner of the galaxy.
"We are not traitors. We are the true loyalists. We swear loyalty to humanity, to the future, and to every soul that refuses to live under the shadow of a tyrant."
"Those who refuse to become slaves, rise up! Stand against the evil tyrant!"
Meanwhile, Lion served as the Supreme Commander of the Federation and directed the Federation's military forces.
Guilliman served as Prime Minister and took charge of the government's administration.
In the first week after taking office, he signed 327 administrative orders.
The Imperium's inefficient star system was abolished. A new Federation administrative division system was established using economic output, military value, and strategic position as three-dimensional coordinates.
It established the first unified system of weights and measures in Federation history, a perfect tax standard, and a unified legal system.
The other rebel Primarchs were also given different positions.
Dorn, as the Guardian, was responsible for building the Federation's defense system. Khan commanded the Federation's mobile strike forces. The White Scars fleets under his command raced across the galaxy at high speed, crushing any forces that resisted the Federation.
Vulkan and Ferrus were responsible for the research, development, and production of the Federation's weapons.
At the same time, the Federation also abolished the Treaty of Olympus.
Scientific technologies forbidden by Imperial law were unsealed. Iron Men and Stone Men were allowed to live within the Federation just like humans.
The Federation's promises attracted countless rebel forces that had barely survived in the shadow of the Imperium.
Many Mechanicus planets chose to betray Mars and join the rebels.
The great Magi wished to further explore the truth and led the full strength of their forge worlds to join the Federation.
For a time, the Federation's momentum was overwhelming.
Its sphere of influence expanded at a visible speed on the galactic map. New planets joined its sphere every day.
Imperial envoys traveled around the worlds, issuing warnings about the Federation's betrayal and evil.
However, Guilliman's propaganda department was more efficient than the Imperial envoys.
The propagandists used various means to show the many human planets throughout the galaxy how prosperous, stable, and full of hope the worlds under Federation rule were.
The worlds under Imperial rule were worlds filled with poverty, oppression, and constant anxiety.
Even the Chaos Gods continuously sent daemons to torment various Imperial worlds, committing evil deeds in the name of the Master of Mankind and causing people to regard the Emperor as the root of evil and to despise the Imperium.
Following Guilliman's advice, the rebel Primarchs including Sanguinius did not rush to attack Terra.
"Time is our ally," Guilliman told his brothers. "With each day that passes while we wait, we will obtain more battleships, more Titans, and more warriors."
"But the Imperium was declining. The Emperor's rule was foolish and cruel. There was no civilization that would accept the rule of a dictatorial and despotic government."
Thanks to Guilliman's efforts, the Federation relentlessly increased its military strength in order to conquer stubborn and unmanageable planets.
The administrative system Guilliman established operated at astonishing speed.
For every conquered planet, an Ultramar management team relocated there within 24 hours.
Basic order was restored within 72 hours. The administrative system was rebuilt within one week. Within one month, the world's industrial production capacity would be fully integrated into the Federation's wartime economy.
Conquered worlds were not plundered. They were absorbed and rapidly transformed into logistics hubs to supply the resources needed for war.
Every time the loyalists struggled to defeat an enemy force, even more enemy forces appeared from beyond the horizon.
The tactical reports of Imperial generals gradually became more concise and urgent, eventually turning into the same sentence repeated over and over.
[Enemy forces exceed expectations. Request reinforcements. Request reinforcements. Request reinforcements.]
Although an online war did not occur, the situation in the new timeline was even worse.
The loyalists' defeat at Ullanor severely weakened the Imperial forces and greatly reduced Terra's authority.
Many neutral planets, witnessing the fragility of the Imperium of Man, sided with the Federation.
The Imperial Guards responsible for palace security were dispatched to various parts of the galaxy to support the loyalists fighting the rebels.
The appearance of these golden warriors boosted Imperial morale.
With overwhelming combat strength they overturned battle situations and defeated Federation forces one after another.
However, even the Imperial Guards, known as the strongest and most elite troops, were exhausted and annihilated by the overwhelmingly large rebel forces.
Before the Federation's war machine, the Imperial Guards were like a mantis trying to stop a chariot. They exerted all their strength, yet could change nothing.
Under Guilliman's command and the protection of the gods, the rebel forces expanded at an unimaginable speed.
The losses the Federation suffered at the hands of the Imperial loyalists could not keep up with the pace of military expansion.
In front of the Federation's recruitment offices, people of every class formed long lines — from the poorest of the hive cities to the farmers of agricultural worlds.
From workers who built worlds to merchants who traveled the void, everyone was eager to join the Federation's military.
It was not out of fanaticism or faith, but because the Federation offered them conditions so generous that they could not refuse.
In order to defeat the Emperor and fight the nameless existence that controlled everything from behind the scenes, the Chaos Gods restrained their own desires and did not excessively corrupt the Federation's system.
This was an unprecedented restraint for the Chaos Gods, but the benefits it brought were also clear.
The Federation's military strength rapidly caught up with the Imperium of Man and overtook it in a very short time.
With enormous funding, countless children of suitable age were selected and transformed into Space Marines through nineteen surgeries.
Every forge world continuously produced war engines and weapons and constructed warships.
In the new timeline, even the Emperor and Malcador openly expressed concern about Guilliman's betrayal during their discussions.
"Number Thirteen can defeat all of us with administrative documents alone."
...
In order to gain the power to fight the Emperor, Sanguinius attacked Molech.
Passing through a mysterious portal, the Chaos Angel stepped into the depths of the Warp.
There, Sanguinius overcame the trials of the Chaos Gods and obtained power sufficient to confront the Emperor.
Guilliman's talents were also highly valued by Khorne.
With the help of the Lord of Blood and War, Guilliman also stepped into the depths of the Warp.
He subdued the daemon known as the "First Murderer" as a trump card against the Emperor.
The Lord of Ultramar also received a revelation that if he could offer the entire galaxy to the gods, he could ascend to become a new Chaos God.
At the same time, Guilliman traveled back and forth among the Aeldari, the Necrons, and other forces, seeking power and knowledge.
Fearing Guilliman's operational capabilities and also fearing that the Federation would gain overwhelming superiority over time, the Emperor finally decided to have Magnus sit on the Golden Throne in his place.
He took action himself and eliminated the rebel Primarchs.
Responding to the Master of Mankind's call, countless Imperial forces gathered in preparation for a decisive battle with the Federation.
Under the Emperor's command, the loyalists swept across the land, mercilessly suppressing the rebels who tried to block the Master of Mankind's path.
In the end, the loyalists assaulted the Baal system, which was being used as the Federation's headquarters.
At this time, the entire galaxy had been fortified by the traitor Dorn.
The surfaces of planets were covered in fortresses. Space was filled with armed space stations, fortresses, and launch silos.
Tens of thousands of defense platforms were embedded in the asteroid belts, each equipped with massive cannons capable of penetrating battleship armor.
Baal's homeworld had also been transformed into a fortress. The entire planet was covered by a massive void shield.
Perturabo, as the commander of the general assault, used the deaths of the loyalists to gradually break through the high walls Dorn had built.
Meanwhile, the Emperor sat in the strategy room of the Emperor's Dream and waged a multidimensional war against Sanguinius.
It is particularly noteworthy that during this battle, several of the rebel Primarchs were not on Baal.
Lion was leading armies to attack the homeworlds of the loyal Primarchs in order to cut off their forces, and had also launched several raids against Terra.
Jaghatai Khan led armies to raid the loyalists' supply lines.
Guilliman traveled across the galaxy, operating the Federation while searching for various ancient weapons, all for the sake of fighting the Emperor.
Through Perturabo's efforts, the loyalists broke through the void defense lines Dorn had built and reached Baal's homeworld.
This was the capital of the Federation and the homeworld of Sanguinius.
If Baal fell, the Federation's morale would suffer a catastrophic blow.
Conversely, if the Emperor failed here, the Imperium would lose all hope of recovery.
Both sides engaged in a gruesome melee on the ground.
Imperial warriors and Federation defenders fought fiercely over the ownership of ruined streets and buildings.
The roar of boltguns, the growl of chainswords, the clatter of power gauntlets, and the screams of the dying intertwined, forming an unending symphony of death.
Titans dueled as giants amid the ruins of the city.
When these sacred machines collapsed, they would execute fatal explosion protocols, releasing dazzling light like a newborn star and a storm that covered everything.
Corpses piled up like mountains. Blood flowed like rivers, forming hills of flesh and armor.
Ground troops had to fight between these "hills." With every step they took, they might step on severed limbs or entrails.
Every time they fell, they sank into a swamp of blood and engine oil.
Smoke and dust rising into the sky blocked the sunlight. The sunlight could not penetrate the thick veil composed of dust, smoke, and psychic residue.
The loyalists gradually gained the upper hand and came to the brink of completely defeating Baal.
However, they unexpectedly learned that Guilliman and Lion were returning to the Baal system with reinforcements and would soon arrive.
Cornered, the Emperor had no choice but to lower the shields of the Emperor's Dream and invite Sanguinius to a final decisive battle.
The Emperor used himself as bait and wagered all the stakes of this war.
He firmly believed that if Sanguinius died, the Federation would immediately collapse and the war would end.
Sanguinius, who had been tempted by the Chaos Gods, accepted the Emperor's invitation. The two of them fought their final decisive battle aboard the Emperor's Dream.
The Chaos Angel Sanguinius was ultimately defeated by the Emperor and completely destroyed.
However, Sanguinius also inflicted great damage on the Emperor. His spear pierced the armor and throat of the Master of Mankind, causing massive bleeding.
Just as the final decisive battle ended, Guilliman arrived leading reinforcements. When he learned of Sanguinius's death and Dorn's death, he smiled.
Everything was proceeding according to his plan.
Without the slightest hesitation, he immediately ordered the extermination of the loyalists and the Emperor.
Guilliman's fleet was far larger in scale than the remaining royalist fleet.
The loyalists were drawn into fierce combat. Their operational airspace was constantly shrinking.
The shields of the Emperor's Dream were deployed once more, yet still seemed extremely vulnerable against overwhelming firepower.
The loyalists were driven to the brink of defeat by the vast Ultramarines forces both on the ground and in space.
Seeing the densely packed rebel warships, the captains were overwhelmed with despair. That overwhelming number rendered every tactic meaningless.
In order to achieve victory, the Emperor dragged his seriously wounded body and led the Custodes and several loyal Primarchs aboard the Macragge's Honour, intending to behead Guilliman.
However, contrary to the Emperor's expectations, Guilliman had received even more Warp blessings than Sanguinius.
He was also the target of the "First Murderer."
The results of switching sides were predictable.
The bold choice of not promoting Black to the Dark Emperor resulted in Guilliman's defeat of the Emperor in connection with the First Murder. The Emperor was seriously wounded and on the verge of death.
In the end, through the sacrifices of the Imperial Guards and the fierce fighting of the Primarchs, the Emperor was able to escape from the Macragge's Honour.
Amid the loyalists' tragic and desperate sacrifices, the Emperor's Dream finally escaped the battlefield together with its master.
After the Emperor was returned to Terra, he was immediately seated upon the Golden Throne to prevent him from actually dying.
Although the Emperor is an immortal existence, under normal circumstances he can be resurrected after death.
However, the "First Murder" had targeted the Master of Mankind.
In this situation, if the Emperor died, he would either become the Dark King or truly die.
Therefore, the Emperor could not die. He could only barely continue to survive.
Witnessing the development of an entirely new timeline, the Emperor was completely astonished.
In this timeline, Guilliman — a psyker who had been defeated many times by Fulgrim, Magnus, and Mortarion in other timelines — had become extraordinarily powerful and killed anyone who stood in his way.
He could conquer the galaxy using administrative documents alone, or overwhelm the other Primarchs with overwhelming logistical support.
At the last moment he successfully deceived another version of himself from a different timeline and ultimately seated that version upon the Golden Throne.
"Why is the Thirteenth Prince an even greater threat than Horus?!"