The war was two hundred years ago, so unfortunately I don't know what exactly started it. All I know is that it began with a man who could create demons out of his own blood. He wielded a demon blade known as 'Overeater' which could take the life energy of those it cut and make it his own. With that blade, his blood, and the evil gods who flocked to support him, he created an army of demons which threatened to overrun the southern continent.

[ He crosses his arms and his expression grows...conflicted. His gaze averts a little. ]

It's not possible to form a treaty with demons from what I've seen. They're manipulative and cunning. They'll lure you in under pretence of being reasonable, but will immediately go for the kill once your guard is down. The gods who command them though... They're certainly able to be bargained with, but you have to be careful about it.