The Pantagruelions is a race of giants, as gentle as they are large. They exist in social groups with emphasis on monogamy and child-rearing. Their reproductive practices are similar to that of humans.
The gruelions came from a laboratory in a disclosed location in the Mid-West of the United States. They are distant genetic cousins of humans, and they were bred for slave labor.
The powers that be turned the gruelion society into an autonomous machine that farmed their own crops and livestock. They resolved internal conflicts using their own methods. They built the megacities, the massive sprawl extending from Louisiana to Michigan. They beat the roads in place. Carved from mountain ranges with plasma torches granite blocks for the hive communities.
How did the humans control the gruelions?
Before puberty the gruelion is diminutive, resembling a human more than anything but for their tough grey hide. Only with the onset of puberty did the gruelion swell in mass. Integrated into the gruelion culture was a rite of passage involving titanium and smart rubber shock collars: the gruelion child reaching puberty was given the collar, thus elevating the child's role in the society. Tightbeam remotes activated the collars when rebellion or violence were imminent. These measures were rarely used, for the gruelions were rather entrenched in their role and never thought to question otherwise.
This practice, buried deep in the gruelion psyche, continued centuries after the fall of civilization. Small pockets of humans, often agricultural cultures farming the fringes of sprawl cities, controlled the gruelions using the decaying, barely understood technologies of their great-grandfather's great-grandfather.
At this point, without the tight rein of pre-fall government, the gruelions had progressed culturally, adding hunting and fishing and taleswapping to their repertoire. Some could even write and read the human tongue. Their masters were weak men who depended on the switch to commandeer cooperation from the gruelions, and in turn, fueled resentment and anger in their wards, emotions that were practically non-existent in the gruelions' formative years.
One day, the seemingly eternal atomic slug reactors failed, the electric lights of towns winking, recorded by the useless satellites orbiting the planet.
The human slave owners realized, with increasing panic, that their remotes no longer worked...