Soldiers can cope with killing
Researchers have investigated the mental health of all of Norway’s Lebanon and Afghanistan veterans. One factor determines whether they struggle after having killed another person.
Taking a person’s life is not automatically harmful to a soldier’s mental well-being if the circumstances justify it, according to a study of more than 14,600 soldiers.
“Killing another person does not in itself seem to be something that goes against human nature, and it doesn’t necessarily harm the mental health of the person who does it,” said clinical psychologist Andreas Espetvedt Nordstrand.
Commander Nordstrand is the head of research and development at the Institute of Military Psychiatry, Norwegian Armed Forces – Joint Medical Services. In addition, he is an associate professor at NTNU’s Department of Psychology.
The results of a new study directly contradict previous theories that taking a person’s life is automatically detrimental to mental health. However, everything depends on the circumstances in which it takes place.
In Afghanistan, there was a relatively high risk of engaging in combat. Photo: Norwegian Armed Forces.
Studied all Lebanon and Afghanistan veterans
Nordstrand investigated the mental health of Norwegian veterans after they had completed their military service. He conducted this study with Professor Leif Edward Ottesen Kennair from the same department at NTNU and several other researchers.
Andreas Espetvedt Nordstrand. Photo: Norwegian Armed Forces.
These include war veteran Ronny Kristoffersen, who was himself shot in Afghanistan, and former chief psychiatrist of the Norwegian Armed Forces Jon Reichelt. The study is comprehensive.
“We studied all the Norwegian Armed Forces veterans who had served in Lebanon and Afghanistan, and identified those who have killed in combat,” said Nordstrand.
There is a big difference between veterans from Lebanon and Afghanistan.
The study therefore included 10,605 Lebanon veterans and 4053 Afghanistan veterans, although only a small minority had killed someone. The researchers then investigated how the experiences during service had subsequently affected the soldiers’ mental health.
“We looked at PTSD, depression, insomnia, anxiety, alcohol consumption and quality of life,” explained Nordstrand.
The results are striking – there is a big difference between veterans from Lebanon and Afghanistan.
Lebanon vets suffered more mental health problems
“Taking a life in combat was a key factor among the veterans who had served in Lebanon. The veterans who had killed someone in combat were more likely to experience mental health problems, increased alcohol consumption and reduced quality of life later on,” said Nordstrand.
But that was not the case for the veterans who had served in Afghanistan.
“For the Afghanistan veterans, taking a life had no subsequent impact on their mental well-being. We did not identify a trend in any of the variables we investigated,” said Nordstrand.
The researchers checked all the analyses to establish whether other exposure to trauma could explain the findings. The difference between the two veteran populations is striking.
In Lebanon, the soldiers’ job was largely to calm tensions and ensure that peace was maintained. There was a risk of engaging in combat, but this risk was far lower than in Afghanistan. Photo: Torbjørn Kjosvold, Norwegian Armed Forces.
He believes the findings reveal something fundamental about human nature.
“There is a widespread belief in society that taking the life of another person goes against human nature, and that this will easily create what psychotraumatology refers to as ‘moral injuries’.”
But that doesn’t appear to be the case.
“Our findings indicate that whether taking a life subsequently has a negative impact on mental health and quality of life is highly context-dependent,” emphasized Nordstrand.
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Completely different situations in Lebanon and Afghanistan
Lebanon and Afghanistan were very different missions, which may account for some of the difference.
In Lebanon, the soldiers’ mission was largely to calm tensions and ensure that peace was maintained. There was a risk of combat, but it was nowhere near as dangerous as in Afghanistan.
Participating in a peacekeeping operation seems to make soldiers much more vulnerable to the aftermath of killing another person than soldiers involved in combat missions.
In Afghanistan, soldiers were much more likely to encounter combat situations with more aggressive opponents.
“Participating in a peacekeeping operation seems to make soldiers much more vulnerable to the aftermath of killing another person than soldiers involved in combat missions.
The expectations of the soldiers and their missions were very different.
We believe this supports the view that it is primarily violations of group norms and mission guidelines that make actions like killing harmful,” said Nordstrand.
If the mission entails a high risk of the enemy acting aggressively, there is more leeway and acceptance for taking a life.
The groups are more similar with regard to other traumatic experiences, such as being in life-threatening situations or witnessing something traumatic.
“But the Afghanistan veterans experience fewer problems from being in life-threatening situations, such as participating in combat. This is probably related to training and preparation, which provide mental resilience in high-stress situations and make it less likely that such experiences will negatively impact the soldiers afterwards.
A canine patrol in southern Lebanon. Photo: Torbjørn Kjosvold, Norwegian Armed Forces.
Clear missions that establish norms
“We believe the findings show that we must be acutely aware of the rules of engagement, expectations, and the mission guidelines we set when sending soldiers on armed missions,” Nordstrand said.
And it doesn’t just apply to soldiers. The same is probably true for other areas where the government has a role in violence, such as the police.
If soldiers know and experience that it is acceptable to kill when the situation demands it, these experiences rarely become a problem.
“These factors collectively create group norms among the soldiers – norms that determine what they perceive as right or wrong. It is these group norms that are either violated or upheld if they find themselves in a situation where they have to kill,” he said.
If soldiers know and experience that it is acceptable to kill when the situation demands it, such experiences rarely become a problem. They are not left with a feeling of having done something wrong. At the same time, killing someone is very far removed from what most people in Norway experience, so soldiers are often particularly careful to ensure that the action occurred within the established group norms.
“The differences between the two groups of veterans in our study enable us to identify what creates protection against and the risk of negative consequences of taking a person’s life. The common factor here is the context in which it occurs. This applies to preparations, both physical and mental, and how society and networks engage with individuals who have killed when they eventually return to Norwegian society,” Nordstrand said.
As long as the mission is clearly defined and it is accepted that it may involve taking lives, the psychological impact is usually manageable afterward. Photo: Torbjørn Kjosvold, Norwegian Armed Forces.
Five years of research
Nordstrand started this project back in 2020, and although the data quickly provided clear answers, it still took five years for the article to be published.
In civilized, humanistic societies, people often dislike the idea that taking a person’s life can be entirely unproblematic for soldiers.
“This is a sensitive topic, and the findings may be perceived as somewhat taboo. In civilized, humanistic societies, people often dislike the idea that taking a person’s life can be entirely unproblematic for soldiers, as long as it happens within the rules of war,” he said.
“We consequently took our time and ensured that we had solid evidence for the findings of the study and the interpretations of the results. I had several different statisticians thoroughly verify the findings,” Nordstrand said.
Determined by mindset
Professor Leif Edward Ottesen Kennair joined the team to incorporate perspectives from anthropology and evolutionary psychology.
Professor Leif Edward Ottesen Kennair. Photo: NTNU
“Traditionally, there has been an argument that war is unnatural, that killing is wrong, and that we expect people to be harmed by it, regardless. I have been sceptical of this tradition,” Kennair said.
He believes the results of the study confirm that the internal group norms, or ‘rules of engagement’, determine long-term effects.
“The mindset with which soldiers approach a mission determines whether they expect, are prepared for and interpret the intense aspects of the role. If they are in war mode and fully aware of it, they will deal with it completely differently. They experience events and actions differently than if they are unprepared or have a peace mentality,” explained Kennair.
The Norwegian war veteran Ronny Kristoffersen contributed as a co-author and brought his personal combat experiences into the reflections on the findings.
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Important to address
“I think it is important to bring evidence-based perspectives on this taboo subject into the public debate,” said Nordstrand.
Nordstrand said this is especially important during the turbulent times in which we now find ourselves, when many nations are increasing their military capabilities and there seems to be a greater risk of involvement in armed conflicts.
“Soldiers kill, and being able to do that is actually a key part of their job. The findings are a clear call to take both political and collective responsibility when sending soldiers on dangerous missions, ensuring that they do not feel as though they have done something that goes against the norms of the society they are part of,” he said.
Reference: Nordstrand, A. E., Noll, L. K., Huffman, A. H., Gjerstad, C. L., Tveitstul, T., Reichelt, J. G., Bakker, L.-P., Kennair, L. E. O., Kristoffersen, R. H., Bøe, H. J., & Wickham, R. E. (2025). Killing in Combat as a Potentially Morally Injurious Event: The Diverging Psychological Impact of Killing on Peacekeepers and Combat-Oriented Troops. Armed Forces & Society, 0(0). https://doi.org/10.1177/0095327X251321389
