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When to Use Force and When to Avoid It

The Psychological Aspects of Killing

Dr. Peter Bradley
Associate Chair of War Studies at the Royal Military College of Canada
Kingston, Ontario

I have been asked to speak to you today about how people can be conditioned to kill. While many of us can understand the ideological, economic and political causes of human conflict, the psychological processes which permit one human being to kill another are a mystery to most of us. My role today is to shed some light on this topic. To this end, I will structure my remarks around three questions.

Q1. Do people have a natural predisposition to aggression and killing? Or, do most people have an aversion to killing?

Q2. What conditions must be present for normal folk to kill?

Q3. What stages do people go through in their psychological reactions to killing?

Question 1. Do people have a natural predisposition to aggression or are most people averse to killing?

The answers are yes and yes. "There is aggression in all of us – men, women, children, babies … But most of us learn to put limits on our aggression, especially physical aggression, as we grow up (Dyer, 1985, 116)". Studies have shown that while people vary in their natural inclination to aggressive behaviour, aggression can be primed in normal people and certain stimuli will make regular folks aggressive. For example, being beaten or witnessing others beat someone can stimulate aggressive behaviour. While most of us can control our aggression most of the time, alcohol weakens our inhibitions in this area, consequently guerrilla armies and fringe paramilitary forces use alcohol and drugs to elevate levels of aggression in their soldiers.

As for the second part of this question, almost everyone can be conditioned to kill. That said, most of us are averse to killing and will only do it with great reluctance when required, and we experience great remorse afterward.

Question 2. What conditions must be present for normal folk to kill?

To overcome the natural resistance that most people have towards killing, four conditions are required – distance between the killer and victim, a legitimate authority who is ordering the killing, moral justification for the killing, and proximity of a respected group who endorses the killing. Killing can also be made easier through desensitization and conditioning techniques. I will now say a few words on each of these elements.

Distance. One of the major obstacles to killing another human being is the proximity the killer feels towards the victim. The closer the killer is to the victim, literally and figuratively, the more resistant the killer will be. The more the potential killer recognizes the victim’s humanity, the more he or she identifies the target as a person just like him or her, the more difficult the killing becomes. Therefore, the more distance that can be placed between killer and victim, the easier it will be for the killer to act. Research has shown that the remorse felt by combat veterans weighs heavier on those who have engaged in hand-to-hand combat than those in artillery units who could not see their targets or pilots who engaged their opponents from long distances. But distance in this context refers to more than just physical distance. Social distance and cultural distance also help the killer deny he is killing another human being. This distance can be created and enhanced by highlighting the racial and ethnic differences of the enemy or by dehumanizing the people on the other side. This is often achieved by describing members of the other group as animals, insects or diseases. Examples along this vein include Slobodan Milosevic who called Bosnian Muslims "black crows" and Rwandan Hutu leader Leon Mugusera who called Tutsis "cockroaches" (Morgan & Novogrodsky, 2005).

Legitimate authority. Most people would think that an enemy soldier firing his weapon would be enough to make the average soldier fire back. In fact, the common reaction is to take cover so as to avoid being shot. Many veterans report that the primary reason they fired at the enemy was that their NCO (noncommissioned officer) or officer ordered them to fire. There are many historical accounts from leaders who stated that they had to continually order their soldiers to fire at the enemy. They reported that the moment they stopped ordering their soldiers to fire, the firing would stop, and would only continue when they renewed their orders to fire. Soldiers are more likely to kill when an authority figure demands the killing. Soldiers are more likely to comply with the authority figure’s demands for killing if the authority is a legitimate authority, if the authority is present or near by, rather than far away, out-of-sight and if the authority figure is respected. Soldiers are more likely to comply with the authority figure’s demands for killing if the demands are legitimate or lawful and if the authority figure’s demands for killing are intense (Grossman, 1996).

Moral Justification. Arguably, the most important element to ensure that soldiers will kill enemy soldiers is some sort of moral justification for the killing. Soldiers need to be able to believe that the killing they are involved in is not murder. Because there is such a strong taboo against killing another human, soldiers who are required to kill, in turn, need a special moral framework which authorizes them to kill and specifies who can be killed, when can they be killed and how they may be killed. Terms like military ethos, professional military ethic and warrior code are some of the concepts employed by military forces to describe these moral frameworks. Some of you may also be familiar with just war theory, a longstanding tradition in moral philosophy that lists conditions which establishes when going to war is morally justifiable and provides principles on how war can be fought in a moral manner.

The Pressure of the Group. Soldiers operating in groups are more likely to kill than soldiers operating on their own. US Army research in WWII found that only 15-20 % of riflemen fired their weapons at the enemy during combat engagements. If these estimates are accurate, 80-85% of individual soldiers armed with rifles or pistols did not fire at the enemy. On the other hand, 100 % of crew-served weapons fired (Marshall, 1978). Crew-served weapons are weapons that require more than one individual to operate. Groups enable killing in several ways. First, the bonds that are created in combat units are so strong that individual soldiers are reluctant to let the group down. Before combat and during combat, many soldiers worry about living up to the expectations of the group. If there is strong support in the group for killing the enemy and the group is nearby, the individual will feel a strong compulsion to conform to the group pressure to kill. Membership in the group helps diffuse the responsibility for killing, which also makes killing a little easier as well.

Desensitization. Desensitization is a process of repeated exposure to certain stimuli for the purpose of reducing or eliminating the emotional resistance to killing. A simple desensitization technique is the use of songs and slogans in basic military training which invoke soldiers to kill. Having soldiers yell "Kill" while striking a target during bayonet training is another example. More sophisticated forms of desensitization can involve a gradual escalation of the desensitizing stimuli. An example of this approach is a method which has been used to train torturers; "Thus they would first assign the trainee to guard prisoners, then to participate in arrest squads, then to hit prisoners, then to observe torture, and only then to practice it (Myers & Spencer, 226)". As soldiers witness killing in combat, they also become desensitized, and their resistance to killing is reduced.

Conditioning. As I mentioned earlier, some research has determined that the firing rates of US Army riflemen in WWII was 15-20%. By the Korean conflict the firing rate increased to 55% and by Vietnam, the firing rate was 90-95%. Some suggest that these increases in firing rates were achieved by employing conditioning techniques in military training. One such technique was to change range targets from the large Bull’s Eye target to life-size targets shaped like the silhouette of a soldier. Some ranges were modified so that the targets would pop up unexpectedly and then fall down when the rifleman hit the target. Another conditioning technique which has been around for centuries is the use of military drills. For example, soldiers are taught that when they come under fire from the enemy they should follow the drill "Dash, down, crawl, observe, change position, fire." Drills like this are rehearsed often and memorized so that soldiers will respond instinctively when the time comes. Some veterans have reported that the killing they took part in happened very quickly. Their military training kicked in, they followed the drills they were taught and killed the enemy in a second or two without thinking very much.

Question 3. What stages do people go through in their psychological reaction to killing?

Studies on combat veterans suggest that soldiers go through about five stages in their reaction to killing (Grossman, 1996). The first stage occurs before the killing and is characterized by concerns that the soldier has about the prospect of killing. This is a stage of introspection revolving around questions like: Will I be able to pull the trigger when the time comes? Will I let my comrades down?

The second stage is the actual kill. Two very different responses are common. While many soldiers can kill, most do so with some reluctance, but the act often happens very quickly because of the extensive training and conditioning the soldier has undergone. The conditioning takes effect, the soldier follows the drills he or she has been taught and the act is completed very quickly. Some soldiers are unable to kill and do what they can to avoid it. To avoid killing, some will attend to the wounded, others supply ammunition to those who are firing at the enemy, others run messages or man the radio sets during engagements.

The third stage can be described as exhilaration or satisfaction. Many veterans describe feelings of intense excitement immediately after combat engagements in which they have killed enemy soldiers.

Exhilaration can be followed by a fourth stage of remorse. This stage can emerge when the killer empathizes with the victim or otherwise reflects on the humanity of the victim. Often soldiers strive to deny or repress this stage, otherwise it is very difficult to continue on in combat.

The last stage is referred to as rationalization and acceptance. This stage can take many years, perhaps even the rest of the soldier’s life, because for some, the remorse and guilt can never be completely eradicated.

Desensitization Influences in the Media. There is now a considerable body of research which shows that watching violence in the media leads to more aggressive attitudes and behaviour. Authors who worry about the amount of violence that young people view on television, at the movies, and in video games (Grossman, 1996) see these influences as a systematic program of desensitization which erodes the natural human prohibition against harming other people. Such writers contend that repeated exposure to violence, packaged as entertainment, in the comfort of one’s home or a movie theatre trivializes the pain and suffering of others and desensitizes viewers to the horror of aggression and killing. Some contend that these influences have contributed to the increased numbers of aggressive assaults we have seen in recent times and where these trends will lead is anyone’s guess.


Let me wrap up by saying that most people are averse to killing. They can kill if the conditions are right, but do it with reluctance. Desensitization and conditioning techniques can reduce this natural resistance to killing. In order to get people to kill, the following conditions need to be established: (1) distance between killer and victim, (2) a legitimate authority who demands the killing, (3) moral justification to distinguish the killing from murder, and (4) group pressure.


Dyer, G. (1985). War. New York: Crown Publishers.

Grossman, D. A. (1996). On Killing: The psychological cost of learning to kill in war and society. Boston: Little, Brown and Company.

Marshall, S.L.A. (1978). Men against fire. Gloucester, MA: Peter Smith.

Morgan, E., & Novogrodsky, N. (2005). "A double-blow to hatred". National Post, 5 July 2005, Page A14.

Shay, J. (1994). Achilles in Vietnam: Combat trauma and the undoing of character. New York: Simon and Schuster.