You create this universe.

This isn't a joke. You all get to create this world. So welcome to the galaxy, no promises that I'll be keeping track of everything. [I'll at least try, okay?]

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Things to Consider;

Tone: Interchangeable, whatever works for your civilisation!

Subgenre: Whatever works, civilisations can have different subgenres, one can be more dieselpunk, or steampunk!

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Focus: Kitchen sink leaning, the universe is big, and multiple narratives can all happen at once, different cultures, species, and thinking patterns are normal. All of these different civilisations should have unique etymology, so make up new words and ideas!

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Extent: Galactic. One Galaxy. The Milky Way itself. Try to make it feel GRAND! The galaxy is big, and SHOULD be big! Species should be unique, not conforming. How did they evolve, and what circumstances made them evolve? How did their features help them to survive?

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Technology: Varying. Mostly concerning Galactic-Era civilisations and intergalactic politics. Don't be afraid to create technologies that are hard to explain, that's part of the magic! Ultimately, I want it to seem realistic in its portrayal, something vaguely plausible, at least. It's not quite the focus, but it's nice to put some light on! How /does/ the technology affect their industries?

^ Classics, like energy shields and FTL drives, are perfectly fine, but think bigger! There should be multiple /methods/, like hyperlanes from Stellaris, or Warp Drives from Star Trek! Be creative, think about /how/ the civilisation developed, and how it would affect their choices in design and future development!

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Cultures: These cultures and ideologies are unpredictable, don't be afraid to get things 'wrong' about this reality, try to develop the civilisation from the beginning of its history, or right after a world-changing event! Go out of your way to make the 'bad guys' as well! No civilisation is perfect, a /true/ utopia is impossible. How did their features affect their society? How did their technology affect their society?

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Time: Arguably one of the more important things to consider; Timelines should be feasible, two decades isn't long enough to cement your position in the Galactic Community, but five centuries is too long to still be using steam engines and bullet casings. Of course, if you can find a way to explain it, it should work nonetheless.

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Politics: It's not Unipolar or Bipolar, there should be /many/ major powers, not just one or two, as it's a Multipolar world! I plan for there to be a Galactic-scale 'United Nations' of sorts, like Stellaris, or Star Trek's 'Federation of Planets'. Smaller alliances should exist as well.

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^ Ask this question as well; Do they get to show up on the map? Were they subjugated by a greater power, and integrated so fully that they may as well be one? Or are they the Major power itself, commanding their subjugates with a steel appendage?

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Conflict: Which one? There are many, whether it be high tensions, an infectious outbreak, or an outright war, the galaxy is dynamic. What are they fighting for or against, and how long have they been fighting? How would it affect society?