Season over season, The Expanse manages to use genre changes to better expand its world and fill in the ideas the novels were trying to communicate - I assume. I mean, this is what the show does, and the show follows the basic beats of the novels.
Season 4 is essentially broken into 4 separate storylines, with two of those storylines having sub storylines.
In the wake of the Ring Gates opening at the end of Season 3, humanity is ready to see what else is out there as the gates seem to be opening onto mostly human habitable worlds. Ships full of eager settlers have begun heading towards the ring in our solar system, hoping to make claims on the 1300-ish other worlds out there.
While Earth, Mars and the Belt ponder how to manage the almost magical occurrence and ponder the inherent dangers of worlds that have never known human kind, there's also the vast wealth that seems just on the other side for the bold willing to risk it all.
Desperate Belters are rushing blockades in hopes of staking a claim before official channels screw them out of opportunity. Meanwhile, Avasarala has been made Secretary General of the UN and is now sort of President of Earth - and with her experience has no interest in moving too fast. She's already barely avoided a cataclysm with the Eros incident, and who knows what's on the other side?
And after generations of Mars trying to terraform and do this the hard way, Martians see 1300 perfectly livable planets suddenly available. And the dream of Mars suddenly seems... not worth it?
The four stories follow