People
The History of Stellar Journey so far
No one, we're all alone, save for one other alien species. (In this part of space at least.) Also, the plot doesn't feature any non-humans, except the precursors.
Otherwise, big civilisations long in the past, though a few of them are still around.
Current Species & Cultures
Humans! Developmentally inclined, expansionist, and somewhat militarist. Biologically pretty much us today, with a few differences. There exists hundreds of thousands of nations in the world, situated on planets, habitats, or even massive once-sublight spaceships. These nations have their differences, similarities, wars, and a million other intricacies of diplomacy.
Needs & Relations
Humans in general - various nations, split and united by ideology, geography, goals, and anything in between.
Precursors - they vibin, stuck on a ringworld in an extragalactic star cluster on the other side of the galaxy by their own doing.