Halo ALT Setting
Halo and RWBY Crossover, this is just the setting of it right now.
Disclaimers: I own nothing, the ones who made them are the real owners
Halo Mainstream Universe
Thanks to slipspace technology Humanity known as the United Earth Government or UNSC was able leave Earth and then colonize various unexplored planets outside the Solar Systems. Soon after Colonization on various has been completed, Humanity can enjoy their time of peace. Unfortunately that didn't last very long since old rivalry never died out and so the UNSC finds itself in an interstellar war against the Insurrectionists, Rebels who wish Impendences from the UNSC or whatever Revolution they want even if they kill innocent people in the process. Most of the Rebels are actually former UNSC Soldiers.
Eventually the war against the Insurrections came to a halt with the coming of advanced Alien Alliance known as the Covenant Empire. The Covenant views Humanity as a front of their Gods which they are referring to be another advance Alien Race known as the Forerunners. The UNSC suffer countless defeats against the Covenant's Advanced Plasma Weaponry but the UNSC did gets some small victories against the Covenant in some battles, the most affective against the Covenant is the Spartan Super Soldier Program that gave the UNSC some edge in the Human-Covenant War. Spartans themselves where actually abducted Children and sometimes War Orphans because the Spartan Augmentation cannot be for enlisted Soldiers such as Marines or ODST for some reason, originally the Spartans was deployed against the Rebels before the Human-Covenant War began. The raging Human-Covenant War eventually led to discovery of a parasite Alien Race known as the Flood, even a Forerunner Weapon known as the Halo Rings which the Prophets who are the deluded leaders of the Covenant believe firing the Halo Rings will converted them into Gods not knowing that the Halo Rings is actually a weapon of mass genocide that the Forerunners used when they are unable to defeated the Flood.
Eventually the Covenant's plans to eradicate Humanity and to fire the Halo Rings was ultimately thwarted thanks to the UNSC and their new found Allies which are the Covenant Separatist who split from the Covenant when they figure out what the Halo Rings really are realizing the so called Great Journey was a lie.
Following the Fall of the original Covenant Empire, what's left of it became splinter factions such as the Covenant Remnant/Storm Covenant and the Banished. Meanwhile the UNSC rebuilds everything that the Covenant have destroyed, plus the Insurrections have returned after being dormant for many years as the Human-Covenant War goes on, lastly the Spartan 4 Program was introduce and this time it's volunteers instead of abducted and orphan Children.
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RWBY Mainstream Universe
This war against Salem all began when she wanted her beloved husband Ozma to be brought back to life when she was unable to accept that he is dead. Asking the God Brothers of Light and Darkness only ended in a complete disaster which caused Salem to get cursed with Immortality and all of the Kingdoms she banded against the Brothers got wiped out of exitances and half of the Moon shattered to pieces when the Brothers departed from Remnant and collided with the Moon. When Ozma was brought back to life he and Salem had 4 daughters in their family, that family life was short lived when Ozma starting to suspect something was not right which resulted in the deaths of their daughters when Salem fired a single blast of energy at him.
After learning everything, Ozma now renamed Ozpin vows to end the War against his former wife Salem by forming the Huntsmen and Huntress even though he knows Salem and is Immortal. But things takes a divided turn because Fear and Paranoia turns friends and allies into enemies, this creates a pointless 3 or 2 way war that leaves all sides that tried to oppose Salem severely weakened and in the path of losing the never ending war against Salem.
But good always prevails.
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Halo Alternate Universe
Like in the mainstream, slipstream technology allowed Humanity to colonize the stars, but the only war that the UNSC is facing is the Insurrection which is the United Rebel Front. The Covenant and the Flood doesn't exist in the Alternate Universe, plus the Spartans here are not abducted or orphan children, they are instead recruits just like the Marines and OSDT.
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RWBY Alternate Universe
In this Alternate Universe, Salem did get cursed with Immortality, but when she banded all of the Kingdoms together to attack the Brothers of Light and Darkness. Instead of how it really happened in the Mainstream Universe, the Brothers instead made their choice to genocide all life on Remnant, Humans and Faunus alike, Salem too was wiped out of existences. After this the Brothers departed for good never to return again and leaving a deserted Remnant behind.
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Some Years Later
Years later after all life of Remnant was wiped out of existences, the UNSC discovered the disserted Remnant and colonized it as their own while their war against the URF continues.
End
Next Chapter, Pyrrha Nikos finds herself outside the city of Vale looks very different from the ones she knows, but she will soon realize she landed in a Alternate Remnant that was colonized by the UNSC.