Steven Pinker's latest big idea is the decline of violence in human history. Several different categories of evidence suggest that the amount of violence in human societies has declined a great deal over the past few thousand years, even taking into account the wars and genocides of the 20th century. There are some problems with comparing the statistics, because while modern history packs most violent deaths into a few great spasms of horror, in the ancient world most violence was small scale, a matter of revenge killings back and forth between neighboring tribes, dueling, and the like. But insofar as we understand the matter, it seems that even a Russian or German who lived through both world wars had a lower chance of dying from violence than a member of the average Bronze Age tribe.
It is certainly true that the rate of everyday violent death has been falling for centuries. The average citizen of western Europe or Japan, born after 1945, has had a vanishingly small chance of dying from violence, far smaller than in any pre-modern society we know about. Americans fret about crime, but even in 1990, at the height of the post-1965 crime wave, our murder rate never approached that of medieval Europe or our own of 1790. Outside of a few great wars and episodes of mass murder, the modern world is vastly safer than any that came before.
I am not so sure about the calculations that show an overall decline in violent death, because I don't have much confidence in the numbers. Consider the slide above, showing the percentage of skeletons from excavated cemeteries that show signs of violence. Yes, these cemeteries reveal a violent world in which many people died violently. But how many? To make any calculation you have to assume that your cemetery is a representative sample of the population, and there is no reason to assume this. Archaeologists never find enough burials to account for whole ancient populations. Usually they find only a few burials, obviously unrepresentative of the society as a whole, and you have no idea why some people were carefully buried and some were not. (Or what happened to the others.) Probably members of any local elite were more likely to be buried, and if that elite was composed of warriors, that would make your calculation of a violent death rate too high. Some societies (including ours) also give extra attention and care to the bodies of soldiers killed in battle, which further skews your sample toward violent death. Because of these issues, I remain agnostic on the question of whether the 20th century was less violent, on average, than the 12th.
But despite these problems with the data, something important certainly is going on. In many ancient societies, it was assumed that all normal men were warriors and killers, whereas I am fairly certain that none of my male friends has ever killed anyone. In many ancient societies, war was the normal state of affairs, whereas now we consider peace the normal state and think all wars need causes and explanations.
Pinker links this change to broader political and psychological changes. On the one hand, the decline in violence is obviously related to the rise of states with police forces and the like, which protect us from violence so that we don't have to routinely kill in defense of our homes and families. It may also be related to the increasing squeamishness (to use a neutral term) or humanitarianism (Pinker's term) that we see in modern people. We are, on average, much less tolerant of killing, torture, slavery, and the brutal subjugation of inferiors than our ancestors were; we are even, in some ways, less tolerant of harm to animals (one of the radically new things about the modern world is the rise in vegetarianism).
There is nothing consistent about these changes. Contemporary Europeans who blanch at the thought of beating a dog eat more meat then their medieval ancestors, who watched bear baiting for fun. Modern Americans who can't imagine striking another person in anger support a government that assassinates Yemenis and Afghans with missiles fired from drones. Violence remains a major part of human life. Yet its importance seems to be declining for most of us. Most people seem to be getting nicer, and that is something worth thinking about.