Here's a full overview and exploration of the events preceding and witnessed in The Expanse. Based on the series of novels by James S. A. Corey (the joint pen-name of Ty Frank and Daniel Abraham), The Expanse is set in the 24th century, in a world where humankind has spread throughout the solar system and colonized planets, moons and asteroids alike. Both in the books and live-action adaptation, The Expanse's fictional history is incredibly rich in detail, charting a course from the present day to the fractious, futuristic years of outer space exploration.
Unfortunately, dates are a scarce commodity in The Expanse, with the exact placement of events on the calendar left deliberately vague. It is, however, possible to discern some sort of timeline from the information provided. As a reference point, The Expanse franchise began as a tabletop RPG under the name 2350. This date correlates with other details in the books and TV series and, therefore, it can be said with a reasonable amount of certainty that the main story of The Expanse begins in the year 2350.
Using that date as a launching point, the centuries between the real-life modern day and The Expanse's far future can be painted in. Ahead of The Expanse season 4, here's a reminder of every major event that's occurred in the story.
The Expanse's Ancient History
The first chronological event of significance in The Expanse's story takes place at least 2 billion years before the start of the series, when a highly advanced race hailing from the far reaches of the galaxy develop a new technology called the Protomolecule. Using the power of this mysterious blue substance, the currently-unidentified civilization build ring gates that allow for travel between solar systems and subsequently become a dominant power. These ring gates appear later in The Expanse season 3's finale.
At an unspecified point in the history of the ring gate creators, the race load up a giant rock with Protomolecule and send it hurtling towards Earth's solar system. This rock takes orbit around Saturn and eventually came to be known as Phoebe, but it would be a while before the Protomolecule itself was discovered.
When The Expanse begins, the Protomolecule creators have already been dead for over a billion years, having been wiped out by a second, more hostile, unseen alien race.
Human Colonization in The Expanse
As far as The Expanse's more recent history is concerned, the first fictional event of note is the arrival of humans on Mars. Many fans cite a link between The Expanse and Andy Weir's The Martian as an indication that Earthlings first set foot on Mars in 2035, however even if this connection is viewed more casually, the colonization must have started around this time in order for Mars to have the billions-strong population that exists in The Expanse's present. Better get moving NASA.
Over the next 100 years, several historic, but gradual, processes begin in Earth's history. Firstly, the effects of climate change, pollution and overpopulation become fatal, pushing humanity out into the stars at an even faster rate. This timing is more or less in line with many genuine scientific predictions regarding global warming.
Secondly, the Earth's governance begins to slowly amalgamate. In The Expanse, Earth is ruled by the United Nations, but this shift didn't occur overnight. The EU becomes the dominant force within Europe (with Britain presumably still arguing over Brexit), an African Union takes charge of Africa and the U.S. enters into a joint economic system with Canada. By the mid-22nd century, these continental bodies sign over to the UN, who act as the chief leaders of Earth.
Several other events occur during this period. Colonization of the Moon begins shortly after Mars, Earth completely depletes its fossil fuels, asteroid mining begins in space and a cure for cancer is discovered.
By 2150, the Martian population is thriving thanks to increased immigration from Earth and has a population of over 100 million. Having developed far enough to become a self-sustaining planet and with generations emerging that harbor no connection to mankind's home world, Mars begins to seek independence from Earth, believing that the relationship is no longer serving their best interests. The UN are having none of it.
In the early 23rd century, Solomon Epstein accidentally invents the Epstein drive, allowing for unprecedented travel throughout the solar system and far quicker trips between Earth and Mars. The two planets share this technology, and an independence deal is reached as a result, leading to the formation of the Mars Congressional Republic and establishing The Expanse's two main factions.
Over the next 75 years or so, both Earth and Mars use the Epstein drive to colonize other areas of the Sol system, inhabiting asteroids such as Ceres and Eros, as well as moons like Ganymede and Phoebe. Realizing that, despite the differences between Earth and Mars, both planets are taking advantage of the system's asteroid colonies, the Outer Planets Alliance (OPA) is formed to represent and fight for inhabitants of the Belt that lies between the orbits of Mars and Jupiter.
Judging by the approximate ages of each character, the Rocinante crew are born between 2310 and 2325. Chrisjen Avasarala takes her position as Deputy Under-Secretary of the U.N. in approximately 2339 and that same year, Fred Johnson earns his reputation as the Butcher of Anderson station. In 2342, the Protomolecule is discovered on Phoebe.
The Expanse Season 1
Shortly before The Expanse begins in 2350, Julie Mao's OPA ship is taken by the Protogen-owned Anubis. Seeking to cause a diversion and drive a wedge between Earth and Mars, the Anubis also destroys the Canterbury, containing protagonists James Holden, Naomi Nagata, Amos Burton and Alex Kamal.
The events of The Expanse season 1 appear to take place over the course of several weeks. On Ceres, Detective Miller is tasked with investigating Julie Mao and becomes obsessed with her case, eventually jetting off to Eros.
The Canterbury's survivors are picked up by Martian vessel, the Donnager, and narrowly escape on a frigate that will soon be renamed as the Rocinante. They liaise with the OPA's Fred Johnson, find out about Julie Mao, and also head to Eros to investigate. Here, the Rocinante crew team up with Miller and discover the Protomolecule in all its destructive glory. Simultaneously, Protogen execute a large-scale Protomolecule experiment on Eros that wipes out its entire population in The Expanse's season 1 finale.
The Expanse Season 2
When The Expanse season 2 begins, Holden and Miller are still recovering from the radiation sickness they contracted in season 1's finale, suggesting a period of a few days has passed in between seasons. The Expanse season 2 once again takes place over a shorter period, but with more interplanetary travel to consider this time around, may push the timeline into 2351.
Mars destroys Phoebe station to avoid the Protomolecule's discovery and the U.N. orders the destruction of Martian moon Deimos as a response to the Phoebe attack. Elsewhere, a joint strike team consisting of OPA members, the Rocinante and Joe Miller target the Protogen-owned Thoth station, discovering more about the Protomolecule. The alliance resolves to destroy Eros to prevent the Protomolecule spreading further, but the substance has now taken full control of Eros and begins to pilot the asteroid towards Earth. Miller convinces the remaining consciousness of Julie Mao to land on Venus instead. The asteroid's journey from its original position in the Belt to Venus should take a number of days, if not weeks.
Following the Eros incident, Protogen stage a second experiment on Ganymede, this time testing out one of their Protomolecule Hybrid super-soldiers and a peace summit is held between Earth and Mars as a result of the attack. Martian Ganymede survivor, Bobbie Draper, defects from Mars to the UN after discovering the Protomolecule conspiracy. The UN sends the Arboghast research ship to Venus. Meanwhile, the Rocinante crew meet Prax among the Ganymede refugees on Tycho and take him back to the destroyed station to find his daughter and investigate the Protomolecule further. These events take place arcoss several days at least.
Avasarala confronts, and is betrayed by, Jules Pierre Mao, and the Protomolecule on Venus disassembles the Arboghast.
The Expanse Season 3
Seemingly picking up almost immediately after the events of season 2's finale, the ramifications of that episode are still being counted in The Expanse season 3. Avasarala is rescued by the Rocinante crew but, in the escalating tensions, Mars launches a missile strike on Earth, killing 2 million people. Over the coming days, the UN's Agatha King and the Rocinante head towards Io, where the main Protomolecule research is being conducted, however, Admiral Nguyen triggers an inner conflict between UN ships over the Jupiter moon. Nguyen is killed in the conflict, but triggers the launch of missiles containing Protomolecule Hybrids before his death. Following these events, Secretary Errinwright and Jules Pierre Mao are placed under arrest for their part in the conspiracy.
The Protomolecule on Venus transforms into a large structure and heads through the solar system, stopping between Uranus and Neptune. This journey likely lasts for a period of months. After coming to a halt, the Protomolecule transforms into a gateway that leads to a Slow Zone. During this time, the O.P.A. is officially announced as the government of the Belt. All three of the system's powers send ships to investigate the Ring, with these journies possibly extending The Expanse's narrative into 2352.
James Holden enters the structure at the center of the Slow Zone, learning the Protomolecule's origin and eventually triggers the emergence of pathways to 1300 different systems.
Interestingly, The Expanse season 4 will likely see a bigger narrative gap between seasons. In the books, and hinted at in the season 4 trailer, the story picks up after years of immigration from the Sol system through the various Protomolecule-made portals. This should mean that The Expanse season 4 begins around 2354.
The Expanse season 4 premieres December 13th on Amazon Prime Video.