Human violence, and especially warfare, is a topic of both deep concern and revulsion.

The suffering and deaths over millennia are staggering and almost incomprehensible. Yet, the level of collective action involved in warfare probably exceeds that of any other human endeavour.

Darwin's On the Origin of Species was a summation of evidence for evolu­tion. It quickly provided the foundation for the study of living organisms. From that point on, once Darwin's work was generally accepted, one had to cast one's thinking, questions and interpretations in an evolutionary frame­work. If warfare was as prevalent and significant in the past as many now feel, perhaps we are on the cusp in the fields of ancient history and archaeology of having to do much the same thing. In other words, should not our thinking, questions and interpretations always consider the role warfare might have played? This does not mean that all historic outcomes were the result of warfare, but its role should always be considered. From big questions - such as migrations or rapid cultural change - to small ones - such as why a site was on a hill or why there was a multiple burial - should we not, if we believe warfare was common, always consider its potential role? Such an intellectual approach will go far in deepening our knowledge of warfare and violence.

Human violence can take many forms from intra-family domestic violence to battles lasting days or months and involving tens of thousands of indivi­duals. In order to understand when and where such violence occurred in the past, much less the reasons for it, it is necessary to examine it in specific detail and depth. That is, we need to have a more fine-grained understanding before we try to formulate sweeping generalities. To lump together an intra-village club fight with the battle of Verdun would seem to be folly at our present level of understanding of either type of violence.

Perhaps the most important distinction with the broadest implications that we can make is that between warfare and intra-societal violence. By ‘warfare' I, and many others who study it, generally mean socially sanctioned conflict between independent polities; that is, collective action by one group against another, without there being a larger overarching political entity, the mem­bership of which includes both groups. This concept of warfare allows one to jointly consider forager raiding parties and pitched battles between chiefdoms and states as manifestations of the same general behaviour. This approach gets beyond the often held distinction between ‘raiding' and ‘true warfare', a false distinction which has hindered rather than enhanced our understanding of the topic. Raiding was every bit as deadly as ‘true warfare' and had just as great an impact on people's lives for millennia over much of the world.

Intra-societal violence can include personal violence, such as murder, or less lethal acts perpetrated on members of one's own group. As discussed below, the complication is what is ‘one's group'? It can be one's close kin, or it can be all those people who come together for common defence and may number in the thousands.

In the recent past, including the so-called ‘ethnographic present', we can define social groups with some notable exceptions.

Once we move into the past, such distinctions about social groups and intra-group rules of behaviour are much harder to find and evaluate. Because intra-societal or intra-personal violence covers a vast range of behaviours, and most are very hard to tease out of the archaeological record, such violence is not the central focus here and is considered only briefly.

Warfare is different. While there were often conventions governing how wars were to be fought, for most of human history there were few constraints on individual behaviour. In some places, areas were set aside for trade with no conflict allowed, or universally accepted tokens proclaiming peaceful intent were used by people transiting hostile territory. Such conventions were relatively minor and few, and if an individual or group broke them, there was little recourse, so rogue behaviour was hard to control and a threat even in situations deemed peaceful. Our present concerns about killing prisoners and outlawing certain weapons are developments of the last several centuries. For the most part, warfare has been anarchic. Anything goes: treachery, killing helpless captives, taking captives and killing a few at a time as you retreat so the enemy is discouraged from following you, torturing and mutilating captives, displaying body part trophies so all know how well you fight, killing the children of women you capture, and other such very unpleasant behaviours are known from archaeology and historic accounts. And killing is the goal, along with the capture of women, territory and treasure. Moreover, there are numerous lines of evidence that show how much warfare existed in the past. Warfare can be defined, and it can be studied archaeologically. Like many topics in archaeology, it is not easy to study, but it can be and has been done successfully.