The Expanse is a hard SciFi TV show, showing a possible not so far away future of mankind which is rather grim than shiny. Earth is overpopulated with roughly 30 billion people, 50% of the people having no job but UBI. Ruling body of the Earth is the UN, which also has its own space force.
The rest of the solar system has been colonized, with Mars being in the mid of terraforming and around 4 billion people, but severed ties to Earth. Mars is losely modeled after the old Rome, and Earth and Mars are more or less hostile against each other.
Third fraction are the belters, people who live in the asteroid belts, mining stuff for Earth and Mars. Due to being exposed to low gravity for a whole life, most of them cannot walk on Earth at all.
As said earlier it's hard SciFi: Earth has no FTL engines yet, and only colonized the solar system. Space ships actually do turn around after having reached 50% of their distance in order to decelerate until their target. If the camera is outside a spaceship and there's a battle, you will hear no noise. There is no artificial gravity like in Star Trek, no inertness dampers, no teleporters, and so on and on... instead a very accurate depiction of gravity in space and other planets. Also no FTL communication technology, so the farer away from home planet so the longer an answer takes.