On and around Holocaust Memorial Day, January 27, we are asked to remember not only the Holocaust but also other terrible acts of genocide in the 20th century, one of the worst periods of violence in human history.

These are horrors we want to protect children from, so why try to talk to them about it? It's a question of not hiding facts. Children must understand what human beings are capable of. This means understanding not only the great achievements of science, culture and society, but also how far, at times, human cruelty can go. Our children need to grow up determined to restrain and forestall that cruelty. So, from early on, they need to start learning how it works. How else can they be fully equipped to recognise the signs of evil, and resist it?

What is our approach? We have no hidden agenda. Our argument is plain and up-front: it's war that makes genocide possible. This is not only because genocide is committed under cover of war or during the conduct of it. The very acceptance of war as a legitimate practice of aggression (or, as it is sometimes called, defence) creates a mindset, a social climate, in which war can also be envisaged as a means of oppression and annihilation. We deliberately train and equip professional soldiers to wage war, and the spin-off is that we also equip callous, fanatic, cold-blooded, criminal, cunning, clever, brutish men, and a few women, to commit genocide. And they do. There are even those who get pleasure out of it.

So talking with our children about genocide means talking about things we all know, problems we all have to solve. Intolerance. Bullying. Violence. Prejudice. Hatred. Victimisation. Fanaticism and extremism. Hunger for power. Using weapons, physical and mental. Armed conflict and war can grow from any or all of these.

We also have to ask ourselves whether the laws we try to make for conducting war have, or ever could have, any real bite. Do human rights agreements have any real power to stop human rights abuses? Human rights abuses are no longer, if they ever were, the accidents of war: they are the tools of it. War is an essentially lawless state of affairs. We need to explain this to children.

What's more, as long as war is regarded as permissible, and prepared for, it will happen. Its apparent 'successes' are all, without exception, short-term. Most lead on to failures (not all of them recorded). Every act of war carries the seeds of another: wars may end, in the messy and damaging way they do, but they don't end war. We need to explain this to children.

We need to tell them that war is not a necessary evil. If we take war out of the picture, we'll be able to discern the real anatomy of a dispute, and deal with its root causes in nonviolent ways. There will always be conflicts, the stuff of life, but without war people will be able to disagree in safety. And genocide will be a shame of the past.