Some sincere apologies would be in order.

"We have done wrong to you, because wrong was done to us. We cannot undo what has been done. We can learn to recognise what we have in common, and build on that."

Either side needs to recognise that as the truth, and say it.

And the rest of us need to recognise that we probably are capable of doing things every bit as terrible as both sides have done to each other. And to recognise that friendship does not mean encouraging our friends in their mistakes.