Article Composition
Right out of the gate, the Norwegian veteran study flips the script on what we think we know about killing in combat. For decades, the prevailing wisdom has been that taking a life on the battlefield automatically scars a soldier's psyche. But when Andreas Espetvedt Nordstrand and Leif Edward Ottesen Kennair from NTNU gathered data from more than 14,600 Norwegian veterans, the evidence told a different story—one where context, not the act itself, calls the shots. And sure, that's gonna ruffle feathers in a society that likes to moralize the brutality of war, but the data don't lie.
Take the Afghanistan veterans, for example. These soldiers operate in high-intensity combat scenarios where the enemy frequently engages, where rules of engagement are explicit, and where the mission objective is clear: defeat the opponent. In that environment, pulling a trigger—or delivering a lethal blow—doesn't seem to leave a lasting psychological fingerprint. As Nordstrand puts it, "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." That's a stark, uncomfortable rebuttal to the idea that killing is inherently damaging.
Now pivot to the Lebanon peacekeepers. Their mission was of a completely different stripe: monitor ceasefires, calm tensions, keep the peace. Combat was a possibility, but it was far from the daily reality that Afghan soldiers faced. And here's where the mental health gap yawns open. Lebanon veterans who had killed were significantly more likely to experience depression, PTSD, insomnia, anxiety, and reduced quality of life later on. The study included 10,605 Lebanon veterans and 4,053 Afghanistan veterans, but here's the kicker: only a small minority in either group had actually killed someone. Yet the psychological disparity between the two cohorts is huge. As Nordstrand emphasized, "Our findings indicate that whether taking a life subsequently has a negative impact on mental health and quality of life is highly context-dependent."
What accounts for this divergence? The researchers lay it out clearly: mission expectations, group norms, and rules of engagement. In Afghanistan, soldiers know what they're signing up for. The mission is combat-oriented, the enemy is aggressive, and killing is positioned as a legitimate part of the job. Group norms reinforce that, that's what you do. In Lebanon, by contrast, the mission is peacekeeping. Soldiers there may follow orders to use force, but the overarching framework is about restraint and stability. When a peacekeeper takes a life, it can feel like a violation of the mission's purpose, like stepping outside the accepted norm. And that perceived norm violation? That's where the psychological harm takes root.
Kennair puts an exclamation point on this with his anthropological and evolutionary psychology lens. He's been skeptical of the notion that war is unnatural and that killing automatically breeds moral injury. His take: "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." Ronny Kristoffersen, a veteran himself and co-author on the study, brought his own combat experiences into the reflection, grounding the analysis in lived reality.
Nordstrand says the takeaway isn't just for soldiers, it's for anyone in a role where government-sanctioned violence is part of the gig, like police officers. "We believe this supports the view that it is primarily violations of group norms and mission guidelines that make actions like killing harmful," he explained. "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."
The study, which Nordstrand began back in 2020, took five years to see the light of day. "This is a sensitive topic, and the findings may be perceived as somewhat taboo," he admitted. "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." But ensure they do not feel as though they have done something that goes against the norms of the society they are part of," Nordstrand said. That's the rub: political and collective responsibility when sending soldiers on dangerous missions.
The PMC-backed Kelley et al. study adds another layer, showing that rumination, particularly problem-focused thoughts, mediates the association between killing in combat and negative mental health outcomes. Among 283 recent-era veterans, those who killed and then ruminated on the experience showed elevated rates of depression, anxiety, PTSD symptoms, and hazardous alcohol use. Problem-focused thoughts was the only rumination facet to mediate all effects, though anticipatory thoughts and counterfactual thinking also played roles with specific outcomes. Beyond mediation, killing in combat still had a significant direct effect on every outcome. Rumination, then, may be an important treatment target for combat veterans reporting killing.
What does this all mean? Simply put: context isn't just a footnote. It's the architecture that determines whether a soldier can integrate a lethal act without long-term psychological wounding. Missions that clearly establish when and why killing is permissible foster group norms that protect mental well-being. Missions where the purpose is ambiguous or where killing feels like a betrayal of the mission's core aim? That's where the risk spikes. The findings are a clear call, to policymakers, to commanders, to society at large, to be acutely aware of the rules of engagement, the expectations we set, and the norms we reinforce when we send people into harm's way. Because ultimately, how a soldier makes sense of taking a life may matter more than the act itself.
