Book Series
In Aria, the Martians were able to stay on good terms with Earth so they could put all their resources into terraforming as intended and went a little bit overboard: Mars has now a breathable atmosphere, but is also under water!
As in the WMG above, Mars stayed on good (or at least on better) terms with Earth, completed the terraforming project and became a bridge to the Belt, as well (just look at the haircuts of Gus and his ex, how cosmopolitan Mars is and their Texan colonists).
- The protomolecule masters aren't dead, but actually either went off to another dimension or "ascended" to a "higher plane of existance".
- There was no "unknown aggressors": The "bullets" are actually safety mechanisms against the abuse of their technology (e.g. the shit the Duarte pulled) left behind by the protomolecule masters themselves.
TV Series
- The protomolecule was eventually tamed enough that the humans who colonized the new System far from Sol used it for their otherwise unexplained Artificial Gravity. Blue Sun is almost certainly descended from Mao's company. The PAX might also have been developed based on knowledge of the protomolecule.
- Since the weapon is cultivated from human bodies, the more dead bodies that arise, the better - and a war provides a very handy source of them. They don't really care who wins as long as they can reap huge profits after the fact.
- Eros in particular meets their criteria. It's explicitly a crossroads, with representatives of Earth, Mars, and the Belt available in quantity. With a resident population of 1.5 million in addition to the transient population, a broad cross-section of humanity (all ages, genders, racial phenotypes, etc.) is available to study how the weapon interacts with a variety of subjects. And the asteroid is easy to isolate, meaning that the spread of the weapon can be contained while it's studied.
- Its heavily implied that the space station behind the gate is a hub, and the rest of the recently opened gates were already established. However, there’s no contact with any non-human traffic going in and out any of the other gates.
- The protomolecule was created by a race that wasn't at the top of the food chain. As, more or less, a simple construction vehicle, it curb-stomped everything in its path.
- Mankind might have been spared the destruction because the gate in its solar system failed to form until significantly later in the universe’s timeline.
- Human colonists will find more alien ruins, and pick through them until they alert another empire.
- Confirmed in the books.
The early history of humanity in All Tomorrows (Mars is colonized and partially terraformed, its inhabitants begin to diverge physiologically from Earth humans due to the low gravity, the Martians begin to see themselves as the future of humanity and Earth as decadent, overpopulated, and holding humanity back, a tense standoff between the two planets ensues, which culminates in a massive war, one of Mars' moons is destroyed, and Earth's population is decimated by a Colony Drop attack.) is remarkably similar to the events of the Expanse. Any differences between the All Tomorrows version of events and the Expanse version (e.g. Phobos being destroyed instead of Deimos, the lack of any mention of the Protomolecule or gate network.) is due to Future Imperfect on the side of All Tomorrows, as its an In-Universe historical text written hundreds of millions of years after the Mars-Earth conflict.
In the books, one of the main factors that motivated Duarte to set up shop in Laconia was the belief that, if he didn't take the actions that he took, other people would use the protomolecule in a much more harmful than he would have. In my headcanon, Duarte believes this because of the time that Project Caliban was snatched right from under his boss's nose.
Duarte helped engineer the Ganymede incident because he perceived it to be for the good of Mars (it would advance their terraforming project and stuff), and then saw their project get hijacked by Earther extremists who nearly got Mars destroyed in the process. He probably thinks Korshunov's death happened because Korshunov wasn't hardline enough, and now he's desperate to ensure the future of Mars. Most of the MCR (a.k.a. everyone who wasn't involved in Project Caliban) has no idea what he had to go through. Then the ring gates opened up, and that gave him an idea...
