This story was originally an Archive of Our Own exclusive one, but since it's difficult for me to write on AO3 and the first chapters were rushed and underdeveloped, I decided to rewrite the story.
RWBY: War For Remnant
A Crash Course Through History
Planets
Remnant is an independant star system with six planets. They are: Atlas, Mistral, Vacuo, Vale, Menagerie, and the Grimm Homeworld.
Atlas is a planet that's technologically superior to her sister planets, with native-developed Atlesian technologies and not a single trace of UNSC tech, a fact that Atlas' leaders take pride in. The capital is located on a floating city and the areas around it are mostly uninhabited, due to horrendously cold, mountainous climates and dangerous wildlife.
Mistral is a culture-heavy planet, not unlike Earth's East Asian nations. Home to Enoch Munitions, the planet's main weapons developer, the planet has a forest or swamp type climate, depending on where you are.
Vacuo is an arid, desert based planet without many unique things about it. Favoring weapons made by Enoch Munitions, the armed forces of Vacuo are adept at gureilla warfare in desert locations.
Vale is a planet with a balanced climate and the most history of borrowing equipment from the UNSC. Unlike the other planets, the elite special operatives known as Huntsmen were created in the walls of Vale's capital, with members forging their own weapons.
Menagerie is the home to the human/animal hybrids known as the Faunus. Given as a token of gratitude for their service in Remnant's Great War, the Faunus see Menagerie as a safe haven from the discriminatory parts of Remnant's population.
The Grimm Homeworld is the birthplace to the antithesis of Remnant's colonists, the Creatures of Grimm. It was destroyed by Valean Huntsman team "STRQ," on the orders of Colonel Ozpin and at the cost of a member.
Technologies
Dust is an energy propellant/weaponized substance found on Atlas. Monopolized on by Atlas, this strange energy source had multiple elemental capabilities and did not work outside of an atmosphere for centuries... until Nicholas Schnee invented Dust that functioned in space. In terms of function, it was highly effctive against the Grimm, but it was largely replaced by other things after the Grimm's eradication.
"Aura" is an energy shield system recently developed by Atlas, providing heightened senses and defense through interacting with the user's soul. This technology is extremely rare, and only a few individuals, all Huntsmen, have access to it.
Scrolls are communications devices developed by Atlas, but used universally across Remnant.
There's more to it, but that'll be too many spoilers.
Groups
The Atlesian Military is Remnant's most fearsome, disciplined, and well-trained defense force. Its General, James Ironwood, takes pride in the fact that it only uses Atlas-developed technologies and equipment, although he used old 21st century Earth weapons as a template for his army's weapons.
The Valean Armed Forces are the second most respected of Remnant's armies, mainly due to the fighting spirit of the Valeans and the Huntsmen. The VAF mainly uses outdated UNSC equipment, with Huntsmen usually making their own weapons.
The Mistrali Defense Force is the military force of Mistral. Using Enoch Munitions-made weapons, they are known for excellent strategies and survival skills in a humid environment.
The Vacuoan Army is the least-trusted of Remnant's militaries. They specialize in guerilla warfare in desert locations, and only a few teams of Vacuoan soldiers can be trusted.
Menagerie's Royal Army is the defense force of the Faunus-owned colony of Menagerie. They may be small, but their ferocity and skill makes them as dangerous as Vale's military.
The White Fang is a terrorist group that was originally a political party. Formed to serve as the political voice of the Faunus, a lack of success lead more radical Faunus to take charge. They are known to use the same equipment as the Valean and Mistrali Armed Forces, and the UNSC considers them to be cultists.
Enoch Munitions is a weapons manufacturer from Mistral. They are known to create weapons based off of 21st century designs, but with radical differences, like all of their shotguns having two barrels by default, or certain assault rifles having twin barrels and twin magazines. [A/N: These weapons are from Outriders, a game that doesn't have any stories on this site, but has really cool weapons.]
The Schnee Dust Company is, like in canon, the system's biggest distributor of the Dust energy propellant. Founded by Nicholas Schnee, the company was singlehandedly responsible for the distribution of Dust throughout the Remnant Star System. With the company's name having been dragged through the mud by his son-in-law, can old Nick's granddaughter Weiss Schnee do what it takes to save the company's soul?
The United Nations Space Command is the galaxy's dominant human organization. Since Remnant is an independant star system, they dislike having to ask the UNSC for favors, and if a Remnantian government official has to get UNSC aid, then they've exhausted all other available options.
The Covenant Empire is the dominant force of the galaxy, having assimilated six races into their empire's ranks, along with having destroyed hundreds of human worlds. A Covenant frigate was recently spotted near Atlas, but can it be confirmed that it was targeting the planet?
The Black Queen is a mysterious criminal organization that not even Colonel Ozpin knows much about. They seem to have hired Roman Torchwick, notorious space pirate, to steal military supplies and Atlesian Dust for unknown purposes.
Prominent Figures
Atlas
General James Ironwood is the head of both Atlas' military and its military academy. As one of Atlas' few noble elites, he tries his best to do what's best for Atlas.
Jacques Schnee is the current CEO of the Schnee Dust Company. A vile man, his selfish actions against the Faunus have made the SDC and its members a major target for the White Fang.
Mistral
Leonardo Lionheart is the headmaster of Haven Military Academy. An elder member of Mistrali society, he has seen many horrors and may may be more susceptible to blackmail than the other headmasters.
Vacuo
Theodore (REDACTED) is Shade Academy's headmaster. I don't know too much about him, but he's prominent nonetheless.
Vale
Colonel Ozpin is the head of Beacon Academy of Military Science. He personally led the operation to destroy the Grimm at their source and continues to defend the Remnant Star System with an array of elaborate plans and the resources and willingness to carry them out.
Glynda Goodwitch is Ozpin's second in command and the so-called "Witch of Beacon." She's a very attractive woman, but her strict behavior and high rank dissuade men from approaching her.
Menagerie
Ghira Belladonna is the chieftan of Menagerie and the founder of the White Fang, before it became radical. He's known to be overprotective of his family.
There's more here, but that'd be too many spoilers.
Sorry for posting an unfinished document, but my tablet was about to die, and I was in a mad rush to post this and I posted it unfinished. Concerning Team RWBY and Team JNPR, I'm organizing them a bit differently. Due to this being a more militaristic AU, I decided to give all the kingdoms (planets) militaries, because while the canon Huntsmen system works for one world, it doesn't work so well in a whole star system.
Freelance Huntsmen still exist, though!
See you at Chapter One!