With a "somewhat evolutionary approach," the in-depth, wide-ranging investigation looks to economic changes, environmental use, technological progress, and social structures as not only prompting war at different times, but also as bringing about changes in the ways wars were waged. The authors accept that the penchant for waging war is innate in human beings. This attribute was not engendered at some point in human evolution. The authors show that violence can be seen in archaeological findings of the earliest groups. The earliest violence was the use of techniques in hunting against other human beings. Human sacrifice, and possibly torture, can be seen in cave drawings. Even the development of agriculture and settled communities did not quell the penchant for violence, but in some ways carried it to the next level. The authors have no political or social agenda--they do not go into implications of their well-substantiated postulate that warfare is derived from inherent characteristics of human beings. Zammit is a doctor and paleopathologist whose knowledge of these fields brings a special insight into signs of violence on human remains and psychology and behavior which are the sources of war and go into war when it breaks out. Guilaine's fields are archeology and social science; which allow him to offer unfamiliar, yet plainly pertinent and unassailable disclosures about societies' penchants for war. With their different perspectives, the co-authors hone in on the core human characteristics accounting for the constancy of war in culture.