The word 'genocide' was coined in 1944 to name a particularly shocking and horrific crime of violence which it was then believed could never happen again. That it has been put into practice so many times in one century is even more shocking.

The human race is the only species that can and does think itself into anger and violence. ('The more I thought about it, the angrier I got.') We ought to be able to think our way out of it too. ('Later I realised that violence didn't achieve anything.')

One much-practised way of thinking one's way to violence is developing beliefs to back it up; some of them may head towards the absurd. 'Violence is the only way to get respect.' 'Violence is the only language they understand.' 'I'm good, you're evil,' 'We're peaceful, they're brutal.' 'I wasn't going to let them beat me.' 'They're ALL cheats/liars/scroungers/dirty.' 'If I took it lying down, I couldn't hold my head up again.' And so on. There may have been a time in the early history of the human race (a time when the natural world was the chief threat to survival) when this kind of primitive thinking served a purpose. But it's nothing but a handicap now.

Genocide is not a wild beast or a natural disaster. It is mass murder deliberately planned and carried out by individuals, all of whom are responsible whether they made the plan, gave the order or carried out the killings. Whatever its scale, genocide is made up of individual acts, and individual choices to perform them. So human individuals need to make the commitment, as early in life as possible, that they will have no truck with it. To do that, the way genocide becomes possible has to be understood.

There follow outline histories of eight 20th century genocides. You may want to research some of them further. There are also pointers towards some of the issues they raise, particularly in respect of their causes. Prejudice, racism, grievance, intolerance, aggression, injustice, oppression - they all start small, and we need to spot and stop them in our own local orbits before they grow and get out of control. This means looking at the often long prehistory of genocide, as well as its symptoms in the present. Understanding these will help to avert future horrors.