( first off let me say that thanos didn't just wipe out half of a planet's population sometimes he conquered and annexed the planet into his territory because he has such a large army they need to live somewhere and he can't have them following him around all the time so now that that's out of the way let's get into the story. BTW this takes place place before infinity war)
Sovereign
high priestess Ayesha was crying overlooking her planet being destroyed by thanos's army. Everything was on fire her people were being killed her military was wiped out and she had no choice but to watch her own people get slaughtered. Eventually thanos's adopted son Corvus Glaive walked into the throne room and saw Ayesha crying on the floor. Thanos wants to see you high priestess said Glaive. Glaive dragged the high priestess to the mothership and she was thrown before thanos on the ground. Good job my son you may go rest we will be leaving soon said thanos. Thank you father said Glaive. High priestess Ayesha your planet is gone your military is gone I will kill half your planets population and now you are here before me said thanos. I know cried Ayesha I know that my people will be killed and I know what you will do after you will occupy my planet for one of your armies and take anything you want from here why do you need me. Because I need you to rule over the remaining as my vassal state. My people will never accept that they would kill me for surrendering said the high priestess. Don't worry my child we will protect you from them and we will also station 800 million soldiers on this planet and yes we will take what we want whenever we want but half of your people will live if you surrender said thanos. Ok if you stop killing my people then I will become your vassal said the high priestess. Good after I do my duty the killing will stop said thanos.
2 weeks later
thanos had wiped out half of the population of sovereign and annexed it into his territory he stationed 800 million of his troops there they were off stealing everything raping every women they could find and killing all who resist thanos's rule originally thanos tried to stop this kind of behavior on many different worlds but decided that high moral was good for troops so he let them do mostly whatever they wanted on conquered worlds
3 years later
by now sovereign was no longer a colony but a satellite state thanos's army made the rules and everybody followed them no question when suddenly a mysterious gate appeared in the capital but fortunately there was a massive base of thanos's troops near and they heard about the gate and sent a platoon of soldiers to investigate. The soldiers arrived at the gate and were in the process of studying it but than it opened and the man in charge called for backup. Suddenly a bunch of humans in Roman armor came and out and started attacking them but their armor was so strong that all the swords and arrows broke against them. The CO ordered his men to open fire on the humans and they were all killed within minutes eventually backup arrived and there were more Roman's and monster's coming out of the gate but thanos's army was far more technologically superior and within 5 minutes the entire expeditionary force was slaughtered with no survivors. The CO reported the incident and it was eventually passed on to thanos himself. This is indeed interesting some kind of portal opening up in my territory. He summoned his son Glaive who was also a general he was the one who led the invasion of sovereign he came into the throne room and bowed before his father thanos. My son something very strange has happened on sovereign a portal has appeared which leads to another planet from what I've been told they are a race that is very primitive and only carry swords and shields. This is strange indeed father should I lead an army and conquer this new world. Yes my son but keep me updated on your progress and you have absolute authority. Thank you father I will not fail you
Sadera throne room
what do you mean that the entire expeditionary force was destroyed said emperor molt. Your highness everything we sent to the other side of the gate has never returned. Summon the senate and war council we need to discuss what to do next ordered molt. ( you guys already know what happens here he sends the allied armies to die so ima just skip this part) by now alnus hill became an impenetrable fortress they had air defense they signaled the location to their fleet who were now in orbit ready to strike at a moment's notice. The Allied army was all on the hill and launched their first attack they were all killed. The second time they didn't even get a chance to react as the entire encampment and the whole allied army was orbital striked out of existence. The gods of falmart saw this and were terrified of this new race of invaders that came through the gate but emroy was in aw of this new race and decided to send his apostle Rory mercury to meet this new race and try to convert them to Emory's religion.
The next few weeks word got around about the allied army's humiliating defeat and how the otherworldlers were committing genocide against humans and not Demi humans ( thanos decided to let the Demi humans live because they were being oppressed by humans and they could make a nice addition to his army) this eventually made its way to the imperial senate and they were debating what they could do to stop them. So far every army they sent have been an annihilated and the very few survivors spoke of how they showed no mercy to any human they were wiping out entire villages families even kids they were slaughtered every human in their path but let the Demi humans go unharmed one of them managed to learn the name of the man leading them general Corvus Glaive who the people nicknamed him the butcher of falmart. Currently the senate was in crisis they were losing cities and towns left and right they were running out of manpower and they were moving to fast to be stopped. Molt had no idea what to do he never fought such a brutal and bloody opponent before his son zorzal wanted to go and fight them but he knew that he wouldn't come back if he did but he let his stubbornness get the best of him and he marched off to face thanos's army. Zorzals head was dropped off in his room 4 days later with a letter saying that he was going to die and his empire will fall by thanos's hands. Molt then eventually figured out that the emperor who's army he was fighting belonged to a man called thanos and he was hoping to make a treaty with him but he needed to win a battle first to negotiate on more equal terms. The gods of falmart decided to meet together to discuss what was happening in their world. So about this new race said flare god of the sun. They are killing our followers left and right this cannot stand. But they are only killing humans said emroy god of war and darkness I think we should just let them the humans have been getting old and besides they don't kill Demi humans so we won't lose all our followers. Even so our powers will be severely diminished said zufmuut god of light and order this cannot be excused we must make some kind of deal with this thanos otherwise we may cease to exist. Hardy god of the underworld and the one who opened the gate said why should we can't we just send our apostles to get rid of them. What would that solve said flare they will simply send more soldiers through the gate and they will be troublesome to deal with. They have weapons unlike anything we have ever seen and we don't even know how our apostles would fare in battle. Let's try diplomacy first with thanos said zufmuut if that doesn't work then we'll figure something out. Ok this meeting is adjourned said flare.
3 weeks later
Rory arrived in alnus hill where she was instantly attacked because she looked human. She tried to attack but her weapon wasn't working against the soldiers. One shot a dart at her which knocked her out and she woke up in an interrogation chamber where she met general Glaive. Rory knew him by his reputation and didn't think he could hurt her but he pulled out something she never saw before. Weird glass shards that somehow pierced her soul and it was excruciating for her she could actually feel it and she was now terrified of Glaive. He asked her why she was here and she said that she wanted to meet thanos on behalf of emroy the god of war. So Glaive pulled thanos up on screen and she immediately felt small she could feel his power through the screen and knew that falmart no her whole world was in trouble. Who are you and what do you want said thanos. Are you thanos said Rory. Yes i am why did you want to talk to me said thanos. I have come on behalf of our gods to make a deal with you said Rory. What kind of deal said thanos we are begging you to leave this world and stop all of the killing of not then the gods will declare a holy war against you said Rory. I have already killed almost half of the humans in this continent but I plan to wipe out all humans from this world entirely so if your gods try to stop me than I will simply kill them said thanos. You would try to kill gods said Rory. It's not the first time I've done it and it certainly won't be the last so here is the deal you either let me kill all humans from this world and become my colony or I will destroy this world entirely your choice half of life or no life at all said thanos. Rory was very scared and so were the gods they had no choice but to accept because they could tell he was serious and would rather live than die so they accepted the deal much to Rory's surprise. Emroy and all the other gods accept the deal thanos said Rory. Little did she know the whole thing was being recorded and broadcast to every village and city in the world via drones and the humans felt abandoned by the gods against this new enemy. Molt also saw the broadcast and felt hopeless and so did everyone in the imperial senate. Thanos's army then dropped a gas in sadera that was genetically engineered to kill only humans they broadcasted this to the entire world they saw only humans vomiting blood and their skin being burned. This terrified everyone and the Demi humans rejoiced and celebrated the humans were finally getting what they deserved. It didn't take long until eventually the entire world was enveloped in this gas and every human dropped dead this world had become a colony of thanos and he now had the power to create gates to other worlds thanks to hardy. General Glaive became the ruler of this new world by blessing of thanos and this world was now a giant military base for thanos's army.