The Cataclysm was horrible. Most do not know how a whole star system can just explode, disappear, or whatever happened.
It was the middle of the 23rd century. Humans, grew up on Earth. As expansionists, they had colonized 1 other planet (Mars) and 3 moons in the Sol System (Luna, the moon of Earth, Europa, and Titan). With additional scientific stations on at a dozen other locations. Their expansionism really showed in their exploration of other worlds. With the introduction of faster-than-light drives, they quickly went off exploring. In addition to the several worlds they made trivial colonies on, they found a lush, rich planet named Legion in what has since been called Olympus System. But not only that, there was an additional smaller habitable planet, and an even smaller habitable moon. Humans even established colonies on other near-habitable worlds.
With the human population exploding, and availability (and encouragement) of travel to other worlds, Legion quickly amassed a population of over a billion, and just before the cataclysm occured, population in the Olympus System broke 3 billion.
The human population across the verse was estimated at about 19 billion on at it's height.
Then the Cataclysm occured. It's still a bit strange, and there are scientists trying to discover what has happened, but after that fateful day in 2265, the human population shrunk the 13 billion people in the Solar System to 6 billion.
It was a trying time for the next hundred or so years of human history, and no one knows if it will happen again.
No plausible theories have been established, but several implausible ones have been presented, including:
- Gravimetrics predicts strange results during an antimatter fusion reconstitution, that might cause such a cataclysm, but the computer models show dramatically different results (like a supernova resulting in a remnant black hole, or a stellar nursery)
- A powerful alien species, or a strange spatial disturbance relocated the system.
- Ultima Division 42 went back in time and neutralized the system using one of their "newfangled doohickies".
So far, all of the theories have been labeled as "Conspiracy Theories" by the reputable scientists, if they garner that much attention.