Attempting to understand the origins of war and peace has a long lineage in international relations. One could argue that Thucydides made the first effort a couple millennia ago. Azar Gat actually embeds his analysis in history well past even Thucydides as he looks to anthropologic evidence to more deeply understand if war is an inherent biological trait of humanity or a problem of our own making. In this way, the book under review here is not only about what causes war but also about the root source of violence itself.

The starting point of any such endeavor seems to be an evaluation of the biology of violence. Is violence endemic among animal species or is it an exception to the rule of peace? One would expect that natural selection would work to remove propensities to kill from a species, as that trait would decrease its long-term survival prospects, but theorists have also long argued about the violent and competitive status of nature. Gat focuses on the more recent biological literature and notes that “innumerable field studies have revealed that lethal violent competition within species in nature is endemic and widespread” (p. 5). Of course, humans may still be an exception, but there are also numerous studies that have shown that prehistoric human groupings were quite violent. For instance, a study of around 9,000-year-old Paleoamerican remains found “violent injuries in 58 percent of the males and 18 percent of the females” (p. 13).

One has to be careful inferring too much from these studies, but the consistency of violence seen across different animal species is likely meaningful. While this does not mean that humans are inherently violent, the weight of evidence seems to weaken the image of the peaceful prestate societies. This is an important conclusion as it shows that violence preceded the state, which is a foundational part of Gat’s argument. There remains a key distinction, however, because even if violence is not driven by the state, it does not necessarily mean that war preceded the state.

Gat acknowledges that violence and war are not quite the same, and this would certainly be true with just about all of the prehistoric analyses. The anthropologic record, then, really creates two new questions. First, assuming that there was violence, what were humans fighting over? Second, what happens when one takes these apparent biological drivers of violent competition and places them in more complex social organizations, which eventually become the modern state?

To answer the first question, Gat dives into the rich psychological and social-psychological literature that has repeatedly examined the sources of human desires and actions. The answer that he settles on is both intuitive and not necessarily new: biological imperative. In other words, individuals are competing over resources that determine their biological fitness and the ability to pass on genes to future generations. As such, it is not surprising that the competition for resources (food and water) as well as reproductive partners sparks violent confrontations. Of course, this is not the end of the story.

The real crux of the question concerning the origins of violence revolves around the impact of complex social organizations. Unlike our animal counterparts, humans have developed a large set of social connections and institutions that can alter individual calculations about violence and cooperation. Gat sees these institutions as less about altering human behaviors than about being designed to enhance the survival of those who control them. In other words, the state is a vehicle that can be used to increase the survival of an individual or group of individuals.

The story, though, is not that simple. The development of these complex social organizations also creates a new set of competitions that can lead to violence: power, security, status, worldviews, pageantry, and play. The importance of these competitions remains tied to the biological imperatives and to the ways in which control of the state satisfies those necessities. These new competitions, however, also raise the stakes as they often involve not just individuals competing but entire societies as well.

If these social organizations can drive behaviors of a large group of individuals, can they ultimately be used to limit the use of violence? Gat’s use of evolutionary theory and links to biological drives leaves open a path to both peace and war. In other words, the drive is to increase survival and procreation (even if society has hid it behind other competitions), but there is no reason to believe that violence is always the most effective path to survival. Violence and cooperation are two tools that can be used to increase survival, and the choice of instrument remains driven by the costs and benefits of each approach.

From this perspective, Gat argues that the recent era of international peace between the great powers has less to do with a changing view of international politics, inherently peaceful views of democracies, or a change in the base desires of humans, but more to do with the economic benefits that modernization has created. In other words, states/individuals can better increase their survival chances with the peaceful benefits of a modernized economy than with more violent appropriations. In this way, Gat offers a new, and more pragmatic, twist on Normal Angell’s The Great Illusion (1910). Where Angell saw the prospects for war virtually eliminated, Gat offers a more tempered view in that the likelihood of war is currently decreased but never far from the surface, given its biological roots.

In general, the author offers a well-reasoned and researched analysis of both the root causes of war and the way that human society and institutions have mapped onto the biological sources of violence. He nicely brings the question down to the individual level and builds up to the larger questions, but this strength also leads to an omission. The state, for Gat, remains a vehicle. It is important inasmuch as individuals can use it to fulfill their needs, but it seems to have no agency in and of itself. While he is clearly correct that individuals can use the state for their own purposes, it appears unlikely that the state has no role other than as a tool for others to control.

This role of the state could range from a bureaucratic model where it is no longer a unitary actor but a loosely connected group of bureaucracies to a stronger version in which the state has its own set of interests that drives its behaviors. When a state goes to war, for instance, is that cost/benefit decision driven by the interests of the state or the interests of those that control the state? Gat seems to imply the latter, which is possible, but it is difficult to completely discount the ability of the state to have its own set of preferences and act accordingly.

Overall, The Causes of War and the Spread of Peace offers a compelling argument as to the biological roots of human violence as well as the ways that human institutions affect the choices to use cooperation or violence to achieve our ends. This emphasis on the biology of violence dovetails nicely with Gat’s use of evolutionary theory to explain both the continued role that violence plays and the choices we made that have changed over time and may change in the future.