Combat Psychology: The Real Impact of Taking a Life in War
- Lidi Garcia
- Apr 4
- 4 min read
The psychological impact of killing in combat (KIC) on veterans’ long-term mental health is a complex topic and depends on the context in which the soldier was deployed. This study allows us to directly compare the effects of KIC across different operational contexts, helping us understand how factors such as rules of engagement and mission expectations influence veterans’ mental health. Understanding these differences is critical to providing better psychological support to former soldiers and developing effective treatment strategies for those struggling emotionally after war.
For most people, killing another human being is a rare occurrence and, in peacetime, considered highly immoral. However, for soldiers at war, such an action may be necessary and even expected.
This contrast between civilian morality and military reality raises important questions about how the act of killing can affect veterans’ mental health. Furthermore, rules of engagement (ROEs), which dictate when and how soldiers may use lethal force, vary by mission and influence the moral perception of killing.
Some researchers argue that humans have a natural resistance to killing their fellow human beings, and that KIC can be an extremely traumatic experience for a soldier. However, other scholars suggest that humans have evolved to use violence under certain conditions.
In this way, the psychological impact of killing would depend less on a natural aversion and more on the context in which it occurs, that is, whether the soldier perceives that his actions are aligned with the norms of the group to which he belongs.
In military missions, ROEs shape the way soldiers interpret their actions and define what is morally acceptable. ROEs (Rules of Engagement) are the Rules of Engagement that determine when, where and how soldiers can use force during a mission. They vary depending on the context of the operation and serve to ensure that soldiers’ actions are aligned with international law, mission guidelines and strategic objectives. For example:
In combat missions, ROEs may allow the use of lethal force against identified enemies.
In peacekeeping missions, ROEs may be more restrictive, allowing the use of force only in self-defense.
These rules directly influence soldiers’ behavior and the psychological impact of the actions they perform. These guidelines vary depending on the mission objective and the organization leading it, such as NATO or the UN.
For soldiers, ROEs are not just abstract rules, but directly shape their decisions on the battlefield, including whether or not to kill an enemy in certain circumstances.
In recent years, the psychological impacts of KIC have begun to be analyzed through the lens of “moral injury” (MI). Moral injury refers to the emotional distress caused when someone performs or witnesses acts that go against their deeply held moral beliefs.
This can lead to feelings of guilt, shame, and regret that are not explained by traditional post-traumatic stress disorder alone. Research suggests that KIC may be a key trigger for moral injury, but the impact varies depending on the context and the soldier’s perception of their actions.
The complexity of studying the effects of KIC is partly due to the unique nature of trauma in war zones. Unlike civilian traumas such as natural disasters or violent crimes, soldiers face ongoing stressful situations, may experience direct threats to their lives, and witness great suffering over prolonged periods. This makes it difficult to separate the specific psychological impacts of KIC from other stressors of war.
This study looked at two groups of Norwegian veterans: those who served combat missions in Afghanistan (2001–2011) and those who served peacekeeping missions in Lebanon (1978–1998). The aim was to understand how different experiences in war, such as experiencing direct threats, witnessing death and injury, and killing in combat, affect veterans’ long-term mental health, alcohol consumption, and quality of life.
Two hypotheses were formulated:
The psychological impact of KIC would be greater among veterans of peacekeeping missions in Lebanon than among veterans of combat missions in Afghanistan.
For both combat and peacekeeping veterans, experiencing direct threats and witnessing suffering would negatively impact mental health, alcohol consumption, and quality of life.
The psychological impact of killing in combat (KIC) on veterans’ long-term mental health is a complex issue and depends on the context in which the soldier was deployed.
The results indicate that for soldiers who served in combat missions in Afghanistan, experiencing direct threats and witnessing deaths had a negative impact on mental health, but killing in combat (KIC) did not.
For veterans who served as peacekeepers in Lebanon, all of these experiences—personal threats, seeing deaths and injuries, and KIC—significantly contributed to disorders such as post-traumatic stress disorder (PTSD), depression, anxiety, insomnia, increased alcohol consumption, and reduced quality of life.
This suggests that the psychological impact of killing in combat may depend heavily on the context of the mission in which it occurred.
The study allows for direct comparison of the effects of KIC across different operational contexts, helping to understand how factors such as rules of engagement and mission expectations influence veterans’ mental health.
Understanding these differences is critical to providing better psychological support to former soldiers and developing effective treatment strategies for those facing emotional difficulties after war.
READ MORE:
Killing in Combat as a Potentially Morally Injurious Event: The Diverging Psychological Impact of Killing on Peacekeepers and Combat-Oriented Troops.
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.
Armed Forces & Society, 0 (0). (2025).
Abstract:
The impact of killing in combat (KIC) on veterans’ long-term psychological health is multifaceted and influenced by deployment contexts. This study compared two samples of Norwegian veterans from combat-oriented (Afghanistan 2001–2011, N = 4,053) and peacekeeping (Lebanon 1978–1998, N = 10,605) missions to examine how personal threats, witnessing death/injury, and KIC uniquely predicted long-term mental health, alcohol use, and quality of life (QoL). In the combat-oriented sample, personal threats and witnessing death/injury predicted negative outcomes, while KIC did not. Among peacekeepers, personal threats, witnessing death/injury, and KIC independently predicted posttraumatic stress disorder (PTSD), depression, anxiety, alcohol use, insomnia, and lower QoL. These findings reveal diverging effects of KIC on veterans from combat-oriented and peacekeeping missions, respectively, suggesting that the impact of potentially morally injurious events like KIC is shaped by mission-specific contextual factors.
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