Thanks for the feedback.
Sacrificing war prisoners was already brought up before and is something we are considering.
Agriculture clearly wasn't a part of the original scope of the game but starts to make sense now given how the game evolved since inception. That's quite an ambitious addition though!
Considering enslavement, well, that's another can of worms regarding both development and public perception, but this would definitely be an interesting move towards realism, that's for sure.