In the distant future mankind creates sentient cybertanks patterned on the human brain to help fight their alien enemies. Then, inexplicably, the humans vanished. They just went away. All that is left of the human empire are the cybertanks who, in their own way, keep the human civilization alive.
I'm not sure if I want to know more about the location backstory, or see where this tale is leading to in the future. Either direction in time is good. This guy can write, and has some fiendish ideas as well!