In On Killing: The Psychological Cost of Learning to Kill in War and Society, Lt. Col. Dave Grossman argues that soldiers, trained to kill, experience psychological trauma from extended combat and killing. It is therefore imperative to recognize the normality of this emotional reaction and to provide support to combat veterans. Originally published in 1995, the book was nominated for a Pulitzer Prize and became required reading for commanders in the United States Marines. Grossman, a former Army Ranger with a degree in psychological counseling, has the expertise to contribute this work of nonfiction to the literature of combat psychology.

This guide uses the 2009 Back Bay Books edition.

Content Warning: The source text deals with the subject of violence and also contains references to sexual violence. Grossman applies the term “killer” to soldiers, makes analogies between sex and killing, and describes the details of, and psychology behind, atrocities.

Summary

Grossman assumes that human beings have an innate inhibition to killing members of their own species. When confronted with a threat from a member of one’s own species, the choices are not only “fight or flight” but also posturing and submission. Grossman supports his assumption with research from World War II claiming that only 15-20% of soldiers fired at the enemy. Additionally, he demonstrates that the weaponry in previous wars should have caused more deaths than those that occurred.

Given this natural resistance to killing, extended combat and the act of killing result in psychological casualties for 98% of soldiers. Psychological symptoms include fatigue, confused states, and even character disorders. Most of the factors contributing to psychological casualties are related to the burden of killing. Psychological stress comes from the exhaustion of combat and the confrontation associated with facing someone who wishes the soldier harm and death. All these factors drain the soldiers’ well of fortitude.

The trauma of killing another is lessened with physical distance. At a maximum range, when soldiers cannot see their victims without mechanical assistance, such as radar, there are no cases of psychological casualties. However, as the distance gets closer, the psychological trauma increases. At close range, where the soldier can see the face of the victim, there is significant trauma. There is an even greater aversion to killing someone with a bayonet, with a knife, or in hand-to-hand combat. Grossman notes that the most killing with such weapons often takes place when soldiers are in retreat because the killers need not look at their faces.

There are several factors that explain how soldiers come to kill. The presence of a commanding officer increases the chances that a soldier will fire upon the enemy. Membership in a tight-knit unit provides a form of group absolution for soldiers who are likely to feel less responsibility for their actions and to feel pressured to conform to the group’s behavior. Leaders work to provide emotional distance between soldiers and the enemy as well. Sometimes, dehumanizing language is used to describe the enemy, creating a cultural distance that makes killing easier. Moral distance is employed as well, as soldiers are told that they are fighting on the side of justice while the enemy is in the wrong. Borrowing from the work of Ben Shalit, an Israeli military psychologist, Grossman adds that soldiers need means, motive, and opportunity to kill the enemy. Lastly, Grossman notes that the predisposition of the soldier matters: 2% do not feel any inhibition to kill legitimate targets and do not suffer a psychological response for doing so.

These factors can lead soldiers to commit atrocities despite the natural inhibition against killing. Grossman analyzes the My Lai massacre in Vietnam by noting the cultural distance created by dehumanizing terminology, the high level of casualties the offending unit had sustained, and the presence of a respected commander. After outlining a spectrum of atrocities, Grossman points to the murder of a non-threatening civilian as the worst case. Atrocities, often done for the benefit of a leader, can provide a short-lived form of mass empowerment but are ultimately self-destructive. Calling atrocities the most repulsive act of war, Grossman seeks to understand them to prevent them.

After World War II, the military began using classical and operant conditioning on soldiers to increase the rate of fire. Classical, or Pavlovian conditioning, uses desensitization and positive association to shape behavior. Soldiers were desensitized to violence by watching extremely violent movies. Operant conditioning, pioneered by B.F. Skinner, provides rewards and punishments for behaviors. Soldiers were trained to shoot at human-like targets and received badges and weekend passes for doing so successfully. With these methods in place, the rate of fire increased to 90-95% in the Vietnam War.

However, soldiers were not prepared for the psychological fallout of killing. Grossman identifies grief stages in response to killing. The soldier kills reflexively, then experiences a feeling of euphoria for that success, followed by remorse, and then finally rationalization and acceptance. Soldiers feel guilty about experiencing euphoria in the aftermath of a kill, even though that is normal. Not all soldiers reach acceptance.

Many Vietnam veterans did not reach acceptance, and a high proportion suffered from post-traumatic stress disorder (PTSD). The military failed to put in procedures to protect the psychological health of these soldiers. They did not receive reassurance, were deployed individually, had no opportunity to interact with peers after their deployment, and were given drugs to treat stress. The war itself was particularly traumatic as the line between combatants and non-combatants was blurred and there were no zones where soldiers could go for respite. These soldiers returned to the US and were met with a hostile public. Some were labeled murderers and spat upon. Grossman argues that this lack of support magnified the trauma experienced during the war. In contrast, World War II veterans were welcomed as heroes, which helped to minimize the trauma of combat. In the future, Grossman recommends that troops not be committed without public and Congressional support, and even then, only if the action is in the vital interests of the US and achievable.

Grossman then draws an analogy between the psychological conditioning of soldiers and that of children and adolescents in the US. Arguing that exposure to violent movies desensitizes young people to violence and provides an association with pleasurable activities, Grossman compares it to classical conditioning. Violent video games, which reward players for shooting human-like targets, are akin to operant conditioning. Role models in movies are increasingly killers. While soldiers in the military are taught to kill only on command, there is no such discipline instilled via media violence. Grossman explains the increase in violent crime via this psychological conditioning. Unless there is a reverse process of desensitization and change going forward, he predicts a dire outcome for the US with escalating rates of violence.