@SweatyBrie "but she can't understand society" Well no, she didn't understand, which doesn't mean she can't. She's more or less a psychopath. "If you kill anyone else human society will reject you and you will be killed" would work on a demon as well as on any psychopath, if you can back that up.
@tuatara1 It might be possible but it would take understanding what the demons want and making it so they can only get what they want without killing humans. The mistake here is thinking that demons are/will be forthright and honest in their desires or that one of those desires is peace. Peace isn't something that can be achieved through negotiation with demons, but by making the conditions of peace preferable for them to the conditions of war. If a human/elf what have you could step into the 'role' of demon-lord it might be possible to hold them in check through the 'natural' demon hierarchy. I'd guess it's just a 'most powerful at the top' pyramid.
@tuatara1 It might be possible but it would take understanding what the demons want and making it so they can only get what they want without killing humans. The mistake here is thinking that demons are/will be forthright and honest in their desires or that one of those desires is peace. Peace isn't something that can be achieved through negotiation with demons, but by making the conditions of peace preferable for them to the conditions of war. If a human/elf what have you could step into the 'role' of demon-lord it might be possible to hold them in check through the 'natural' demon hierarchy. I'd guess it's just a 'most powerful at the top' pyramid.