Approximately 50,000 years before the story, sometime during the third millennium, mankind was almost driven to extinction by a global apocalypse brought on by a nuclear World War prior to the events in Empire of the East.
The role of post-apocalyptic technology in creating a magical mythological society echoes Saberhagen's Berserker series.
[6] An intelligent supercomputer, ARDNEH (which was formerly part of an American nuclear response system), initiated a physical change to the structure of the world.
By the time the events recorded in The Books of the Swords occur, ARDNEH has passed into legend, worshiped as a benevolent god.
[7] The gods, having become bored with mankind, created Twelve Swords of Power, and scattered them throughout the world, as a grand game of survival of the fittest to be played out on earth.
The demons of Saberhagen's Swords universe are the remnants of atomic or other high-power weapons detonations, rendered anthropomorphic by the Change.
All demons have a "source of life", which is usually hidden within a fairly innocuous object like a mirror, charm, bottle, or weapon (compare to djinn).
The Red Temple provides and controls much of the traffic in prostitution and drugs, although they also encourage free love, gambling, gluttony, and excessive drinking.
"[8] Novelist Dan Wells credits Saberhagen with inspiring his own writing aspirations, and praises the series' combination of the "stunning imagination" of fantasy with the "logical" plotting of science fiction.
Despite noting that the worldbuilding is sometimes underdeveloped, Wells praises the series' "addictive brilliance" in building and then resolving the swords as interlocking "logistical puzzle[s].