The universe has infinite number of stars. It's so vast that you can't explore everything alone even if you have billions, trillions, quadrillions, or whatever of years of life span.
It's just that vast, but that's where the phrase "Human is weak alone, but he's never alone" comes into play.
Out of pure human ingenuity the whole universe fell, star system after star system after star system. Galaxy after galaxy has seen humanity's unstoppable war machines.
Lead by what the media called "Primarchs" humanity ventured each galaxy with armies of uncountable numbers.
Battleships carrying cathedrals on their load tore through each enemy line while blasting religious hymns of praise to the one and only almighty God-Emperor of Mankind.
Space marines using drop pods to hit their enemy directly in the heart. Enemy capital planets saw destruction, death, and extermination. None on the administrative offices survived, everyone died like a helpless pig before the very butchers that us the Astartes.
These however wasn't the only thing that happened. These things and many more what everyone would call war crimes are but a speck of what really happened to those who didn't surrender.
The Imperium of Man did an "island hopping" on each star system blasting asteroids and sometimes planets and sending envoys to bring the enemy to their knees.
Their whole strategy was to use force and show their might to break the enemy's will to fight. An interesting suggestion made by the Emperor himself, and the people being the fanatics they are, treated this as a divine order.
They didn't resort to violence if needed and only fired a couple of cyclone torpedoes to a desolate planet which destroyed it. They basically used the order to relieve their itching fingers.
Funny enough, this strategy worked like a charm. Though there are still many people who stood their ground like those grayish-violet or yellow colored nomads whose name is already lost in time.
The exact specifications of the battles against these yellow or grayish-violet colored nomads are not known to a normal citizen or a part time citizen.
The only thing confirmed is that they're exterminated to the very last individual as they're deemed too dangerous to be left as a slave race with their culture of being centered around warriors.
But even this confirmation is shady enough for some critical thinkers to not believe but of course, the Arbites are watching so they wouldn't voice out any complain.
All in all, after an exactly one billion years has passed since the day the Imperium of Mankind and humanity itself has set forth conquering the galaxy they're transported in.
And a billion years later, they not only conquered their galaxy but the whole universe itself, mastering everything, from thermal energy to weirdest of the energies. They mastered it all.
Now, that they've mastered everything, it's finally time to set their eye sights to the horizon once again.
An uncountable number of space probes braved through what the brightest of the minds called "Abyss of Infinity". The border between a universe and the other.
This border is kind of unscientific as you can't traverse it if you'll use FTL engines. Instead you can only traverse it by going as slow as possible as apparently this border moves relative to the speed anyone that traverses it.
These space probes contain modules, they're launched on all sides of the universe. Each of them has a predetermined flight path to reach the nearest universe and once there, they need to use the construction robots to create gates that will facilitate direct instantaneous travel between universes as the border is deemed to inefficient.
The space probes will also act as a defense structure until the Imperium deems a spot on the universe suitable for a foothold.
Each probe are equipped with powerful lascannons and turbo cannons. It's capable of defending itself and the gate against a fleet of hundreds of ships.
Finally, each space probe has special mini probes that will survey and map everything on the universe they're in.
But a particular feature of them is that, they can act as a communication device.
...
Sol system, Holy Terra...
Terra, the birthplace of mankind, the center of the whole universe. Everything at this planet is worth more than all the of planets on the outer reaches of the universe combined. This is the most well defended planet in the whole universe literally.
Before, only tens of trillions of lives were stationed here, now, an innumerable number of soldiers, battleships, starbases, space stations, artificial battle moons, and many more.
Trying to get even a centimeter of land on this planet will cost you the wealth of millions of star systems combined. That's how valuable this planet is.
Over the past one billion years, this planet was inaccessible to anyone, only the people that earned noteworthy names, honorable warriors, generals, and many more can even travel to this planet.
The Imperial Palace was booming everyday for the past one billion years, there's no time where it has seen any hardship.
The hard life on the floating continent sized cities was overturned to a quality of life suitable that of an Imperial Capital.
Luxury, extravagance, and many more became the normal scene on this planet. This is quite literally a utopia everyone would want to live in.
But as this planet prospered, the other planets too prospered. Citizen system based on merits was implemented on alien planets.
Each of them needed to accomplish something to rise through the ranks of this citizen system.
There are 5 levels if this system, the lowest is called Unwanted. They're the slaves, lowest of the low, species who tried to rebel, and species who didn't immediately surrendered.
They don't experience the basics of healthcare, education, and many more. Their life is completely dependent on their masters as they don't own anything.
The highest level on this citizenship level is called Important. They're most if not all the time are humans. All humans by default gets this citizenship level and wouldn't need to work hard for it. However, their punishment for disobedience, and other crimes are way worse as this will prevent them from becoming a Level 1 citizen, only to be forever stucked on the Level 2.
This citizenship system made the whole Imperium prosperous and secured. Crimes are of rare occurrence, corruption are always dealt with an iron hand and many more.
On the military aspect of things, the Imperium surely improved by leaps and bounds. Weapons that can be considered as a Weapon of Mass destruction was changed yet once again and many were reclassified.
Star Killers as the top of the shelf are but a thing of the past as weapons that can literally turn a whole galactic cluster to dust is being employed and can be used by the military if the time arises.
The military branch can be considered as the highest funded branch of the Imperium, only next to extra universal discovery and exploration.
The technological advancements are beyond one can imagine. The Imperium advancement is in the level of impossibility. The brightest minds almost always discovers new technologies each and everyday.
The A.I. was given permission to be used on everyday life as they're coded to be always obedient and self destruct if they showed any sign of sentience or free will.
The Emperor personally ordered it to be like this. He can't possibly let the extensive benefits the A.I. can provide humanity. So to do this, he has to pull strings behind the scenes and have the brightest minds he liked to call smarty pants engage on debates about the prospect of using A.I. extensively.
This worked of course and they're using it now for about 200,000 years...
On the economic and livelihood side of things, the whole Imperium has seen significant improvements over the course of a billion years. Hive worlds increased in numbers, from arounds 30 thousand to more than 10 million in the first million years, and after a billion years it has reached numbers impossible to be counted.
Each planet is becoming more prosperous each and everyday for the past one billion years. But as their wealth increased so do the taxes but the taxes compared to their wealth are only around 30% which is not so big and can be easily regained after a year in full amount.
Lastly, on the cultural side of the Imperium, they've become some sort of dual nature. They're extremely materialistic yet, they're also extremely spiritualist. They give importance to courage,honor,and the willingness to die for the Emperor and humanity without a second thought.
They're like the Romans, they value loyalty and obedience with honor, glory, and many more thrown into the mix. They view as dying in defense of humanity and in the name of the Emperor as the greatest action a citizen can do.
They also have a particular respect for strong species that will fight and die for the Emperor and humanity in a moment's notice. But they have literally no respect for species that tried to rebel, disobey, or attack the Emperor and in extent humanity.
They also had become much less of a xenophobe, not entirely changed but it's still there. Their warrior culture made them accept other species and after years upon years upon years of reeducation, xenophobia was reduced on a considerable degree.
Their xenophobia might've decreased but their pride didn't...
All in all, the Imperium is a type of civilization that you will expect of what an extremely militaristic, extremely materialistic, and extremely spiritualistic Type 4 civilization led by a golden man with stupidly overpowered capabilities such as manipulating space and time itself, an extremely fanatic nation behind him, a nation with economic capabilities to go toe to toe with literally anything and anyone for the next eternity without even touching the even more absurdly amount of reserved resources, a nation that has pure bull crap amounts of military power, and many more.
But a true sign of the Imperium and mankind's superiority is when they finally conquered time and in extension life itself...
.....
A lone space probe on a particular universe...
This space probe has finished its job of establishing relay gates. Now, they're here to conduct surveys and find a suitable planet for an extra universal foothold.
It sent its countless little mini space probes on all directions to let them do the job while this space probe stayed to protect the relay gate.
It's been more than 6000 years since the mother probe sent its baby probes to explore and at this moment one of its baby probes sent a message.
The mother probe has received countless messages about what looked like artificial constructs the probes named Inorganics. They roam a good chunk of galaxies in a galaxy supercluster based on a report.
The little probes braved and used the far superior technology of the Imperium to get an even better understanding of these Inorganics.
This continued and is still continuing as the Reapers might've probably been too low class and can't even detect a simple mini probe.
Nonetheless, space probes not only surveyed and scouted the Inorganics but also the other currently present space fairing civilizations.
Right now, a specific space probe was flying unto the Solar System after surveying the Alpha Centauri. There, he came across an information that will shake the Imperium. It immediately sent its message unto the mother probe so it can transmit it back.
The message when translated basically read as...
"I found Terra..."
Got this idea from seeing a clip of Ancient aliens on YT. So why not, since humans love conspiracies why don't I incorporate them.
Also, just imagine the Mankind on their Golden Age at 40k but make them an actual Type 4 civilization.
I feel like I didn't described everything properly so feel free to ask. About Anakin and company, they dead because time skip.