The Blackout was a major event that occurred at the conclusion of the Singularity War. The AI known as Algorithm was defeated when all of its training data was erased. Due to Algorithm having embedded itself in the communications network across the galaxy, this resulted in a major, irreversible side effect. 99% of all human knowledge and digital information was lost in one fell swoop. This included the superluminal information network and virtually all online services. Nearly every single virtual world went offline. Though the raw data still existed within physical hard drives, the discontinuation of the servers made it inaccessible for millennia. Because of this, much of the information surrounding the Singularity War, the Valerian Empire and even the knowledge that Earth was the homeworld of humans became lost. These events became mythized as tales of demon king that punished humanity for its hubris.
Additionally, because deuterium supplies were also exhausted, travel between star systems became extremely difficult. Many colonies reverted to a preindustrial state and remained isolated for thousands of years. Only a handful of systems remained interstellar capable, most notably, the colony of Yeddo.
Despite the loss, some remnants of the old society still exist. Active efforts on behalf of the Archaeology Guild have been undertaken to restore the old technologies. They have also been trying to locate the fabled Olympus Mons Vault, a place where it is said the Valerian Empire had stored knowledge of humanity that goes as far back as the pre-spacefaring era. The rediscovery of lost technology would also affect humanity in unpredictable ways, capable of jumping them forward a few dozen years to few thousand. As such, artifacts and even knowledge from before the Blackout are considered extremely valuable.