Social scientists have come up with many different definitions of war over the years. But the definitions put forward by anthropologists generally envision war as a particular type of political relationship between groups, in which groups use, or threaten to use, lethal force against others to pursue their goals. Therefore, war is distinguished from other types of hostile or violent behavior in that war is waged by organized collectives rather than individuals, and for collective rather than merely personal ends. Defining war in this way has the fundamental implication that the causes of war must reside in the nature of these communities and not in the individual.
Anthropologists have tended accordinglyto reject theories based on the notions of a death impulse, murderous instinct, or some other innate destructive or aggressive predisposition. Such theories are useless in answering the kinds of questions that anthropologists have considered central: why the frequency and intensity of war vary across time and space; why war does not occur at all in some societies; and why, where it occurs, it assumes many different forms and meanings. It is true that theories driving aggression, which imply that activities such as sports, games, or rituals could function as non-violent outlets for aggression, could explain the absence or low incidence of war in some societies. But the evidence seems contrary to this: there is, for example,
The dominant theories of war in anthropology are materialistic and view war as a type of competition for scarce resources, although opinions differ as to what these scarce resources are. For anthropologists, influenced by sociobiology, they are opportunities for mating and reproduction, and the causes of war reside in the competition between individuals for an inclusive aptitude (for example, Chagnon 1990). This approach is essentially a contemporary substitute for the older “killer instinct” theories and suffers from the same weaknesses inherent in all biological explanations. Another school, the most influential and prolific, takes a perspective from ecological anthropology and considers that the opportunities of the earth, food and trade are the key scarce resources (eg Ferguson 1984). Some of these ecological studies are functionalist, arguing that war can play a positive role in some circumstances by redistributing populations relative to environmental resources.
The common element of all resource scarcity theories is that variations in the incidence of war must be explained as the result of rational calculations of costs and benefits by the protagonists (with some uncertainty as to whether these actors are individuals or groups) . In any case, war occurs when