Genocide is much discussed and poorly understood. It is regularly decried, yet little is done to prevent it. It is seen to be one of the most intractable of modern phenomena, a periodic cataclysm that erupts seemingly out of nowhere, often in distant places – Indonesia, Guatemala, Cambodia, Bosnia, Rwanda and Darfur – where ethnic conflict or hatred is said to have spun out of control. So we can do little about it. Bill Clinton said as much while Serbs were slaughtering Bosnians: ‘Until these folks get tired of killing each other, bad things will continue to happen’.

Perhaps we fail to prevent genocides not because they cannot be stopped, and not just because we lack the will to stop them, but because we have misunderstood their nature. Perhaps if we understood genocide properly, a feasible path to stopping this scourge of humanity would become apparent. It may seem bold to say that we have not understood genocide. But, after studying the subject for decades, that is the conclusion I have reached. Genocides are so horrifying, so seemingly in defiance of the ordinary rhythms of social life, so threatening to what we believe we know about ourselves and the world – so out of this world – that we do not think clearly about them. We need to start over and rethink their every aspect: what they are, how they begin, how and why they end, why they unfold as they do, why victims are chosen, why the killers kill, and, most of all, what we can do to stop them.

Even something as fundamental as the real extent of the problem is unknown. Since the beginning of the twentieth century, mass murderers have killed more, perhaps many more, than 100 million people – a much greater number than have died as a consequence of conventional military operations. So genocide is, by this fundamental measure, worse than war. Furthermore, people tend to think of our era's mass slaughters – of Armenians, Jews, Kurds, Bosnians, Tutsis, Kosovars and Darfuris (not to mention recent history's long list of less-well-known mass murders) – as discrete, unusual events. This is wrong: large-scale mass murder is a systemic feature of modern states and the international system, and that is how we should begin to treat it.