The World Until Yesterday considers what we in modern societies can learn from the few remaining traditional societies. Most of his examples come from New Guinea, where Diamond has spent a lot of time over many years. Diamond doesn't fall into the trap of romanticizing traditional societies. He reminds us that as horrific as modern warfare can be among "civilized" nations, at least people in the developed world can, for the most part, travel unobstructed almost everywhere without fear of attack by enemies. That is not the case in many tribal cultures, where people live very circumscribed lives, often unable to travel outside their clan's territory, otherwise they are likely to be killed by members of neighboring tribes. These small scale wars can go on for generations, taking a toll proportionately larger that we experience in the modern world even during the worst wars.
On the other hand, traditional societies may have some better ways of resolving disputes than our courts and procedures. In a chapter comparing dispute resolution in modern and traditional societies, Diamond tells the story of how an accident causing a boy's death was handled between the residents of two nearby villages in New Guinea. In resolving this dispute the paramount concern was not determining who was at fault. Instead, everyone in both villages was worried about preventing a blood feud, restoring trust and equanimity between the peoples in the adjoining territories, and compensating the family of the victim. To do that, the families and others involved have to meet. Apologies must be expressed in person. Compensation must be paid.
These concerns are not adequately addressed in modern systems of justice, which are impersonal and rule-bound. Our highly developed legal system has a lot of advantages over the traditional systems that deal with conflict by engaging in endless cycles of revenge, fomenting distrust of those outside the tribe, and elaborate and costly rituals needed to preserve peace and make amends. Our system of justice might keep us from killing the people who have wronged us (most of the time). But it also leaves us with a lot of hurt feelings and resentment. And a sense that we frequently have not solved the underlying problem.
The solution is mediation of course, which tempers the cold calculations of modern legal systems by introducing elements of communication, understanding, agreement, restoring trust, and making amends. We can view mediation as one effort to bring the values of tribal societies, where the ability to get along with one's neighbor's is critical to survival, to the modern world. Mediation can be seen as one example of learning from traditional societies and restoring practices to modern culture that we have almost forgotten and lost.