Start from common ground instead.
Middle ground is a compromise. It occurs when parties trade off demands, foregoing some to keep others. It only addresses the symptoms of the conflict, not its causes. It doesn’t account for imbalance of power between two negotiating parties. In situations of extreme conflicts, middle ground only hides tensions till they boil over again.
Common ground on the other hand focuses on a set of things different parties share. When parties acknowledge the aspiration, stories and fears of the other side they better understand the causes behind the conflict. When parties see they are pursuing the same interests and needs, it is easier to develop solutions to resolve the conflict.