Why Soldiers Kill

In 1753, Frederick the Great had a secret manual printed entitled The General Principles of War. The Prussian king was anticipating another war against Austria over the province of Silesia, and he thought it wise to instruct his generals on how to handle their troops. He was convinced that both the discipline and well-being of his soldiers would be the decisive factor between victory and defeat. He stressed the importance of providing his men with a steady supply of beer and schnapps.

“When one intends to undertake an expedition, the commissariat must have plenty of beer brewed and brandy distilled along the frontier,” he wrote. “As soon as the army is in enemy territory, one must immediately seize all breweries and distilleries found in the vicinity of the army.” Alcohol was intended to boost courage, morale and group cohesion while also helping soldiers cope with stress, exhaustion and boredom. And it was useful for another reason as well: it made killing easier.

Regina Surber is a philosopher and postdoctoral researcher at the University of Zurich (UZH) who focuses on the ethics of war and peace. Her central question is whether this is morally permissible. Her research doesn’t focus on intoxicants, but rather on military training that enables soldiers to kill. Fundamentally, they are part of the same moral question: is it acceptable to remove people’s inhibitions about killing others?

Humans have conducted organized warfare for roughly 14,000 years – a relatively short timeframe in human history. By comparison, Homo sapiens have existed for 300,000 years, and our earliest ancestors for as long as three million. Archaeology, anthropology and evolutionary biology tell us that the shift to settled life – and the emergence of property and social hierarchies that came with it – has been one of the main drivers of organized warfare.

Interestingly, neurobiology has demonstrated that when people without neurological illness are violent, they use the same brain regions that activate for fear, disgust or shame. In other words, violence is not an instinct like eating or reproduction. It’s not something that people enjoy naturally and is usually in response to a perceived threat.

War is not in our blood. After the Second World War, the US military historian S. L. A. Marshall spoke with thousands of soldiers from around 400 infantry companies in the US Army. His astonishing finding: fewer than 25 percent of the soldiers had actually fired at the enemy. The rest either did not shoot at all or deliberately aimed to miss.

Then there are the well-known experiments by US psychologist Stanley Milgram, who instructed participants to give students electric shocks whenever they made mistakes. Participants were unaware that both the study director and the students were actors.

Remarkably, very few participants broke off the experiment, even as the shocks grew stronger and the students begged for it to end. Milgram concluded that, under certain conditions, most people are willing to inflict severe violence because they tend to obey authorities rather than listen to their conscience.

“What’s fascinating and rarely cited, however,” Surber says, “is that people didn’t deliver the shocks when the study director gave no instructions, or when another person present told them they were free to stop.” When the director merely stepped out of the room, or when participants sat in the same room as their “victims,” far fewer participants continued to use violence.

Although some of these studies from the 1940s and 1960s were later called into question over their methodology, there is broad agreement among researchers today that humans have a natural disinclination toward using violence. Armies themselves have proven this indirectly. The US military is known to have revised its training based on studies like these.

“After the Second World War, the US army began to train soldiers specifically to increase firing rates,” Surber says. The training worked. According to one study, 95 percent of American soldiers in the Vietnam War fired at other human beings – roughly 70 percentage points more than in the Second World War.

“That the training had such a clear, direct effect seems to confirm just how strong our natural inhibitions are,” says the philosopher. Her work draws on findings from other disciplines, including archaeology, evolutionary biology, neurobiology and military history, and she has experts vet them beforehand.

Surber suggested that we meet in the garden of UZH’s Center for Ethics in Zurich’s Seefeld district, where she works. Her teacup is resting on a small stone table, and she herself is perched on the edge of a waist-high wall. She keeps pausing, sometimes for a long while, to gather her thoughts. When she does speak, she gets straight to the point.

“Combat training of this kind, which other researchers and I refer to as mental and physical conditioning, makes it possible for soldiers to kill repeatedly and systematically,” she says. This is one of her main observations, which she lays out in several of her papers. “For me, this raises the question of whether this sort of conditioning can be morally justified.”

To learn more about these training methods – which are also described in numerous studies – Surber spoke with a former US Army officer during one of her stays in Oxford. The physical drills include shooting at human-shaped targets that fall over when hit, conducting combat in realistic model towns and training with computer simulations.

Countless repetitions are meant to make killing routine. Surber says that the mental conditioning is just as important as the physical kind: by attempting to convince soldiers that killing enemy soldiers is not wrong per se, and that combat is about aggression, conquest and dominance, the military tries to limit or bypass their men’s innate capacity for moral judgment.

Surber’s work leads her to conclude that military conditioning may violate soldiers’ human dignity, and she proposes outlawing such training under international law.

In our conversation in the cozy garden, Surber explains why her conclusions ruffle feathers among some of the big names in her field: “I’ve found that popular theories of the ethics of war are built on a fairly unrealistic picture of war and of human beings. If I assert that all elephants have five legs and then draw conclusions about those elephants, it doesn’t tell us much about elephants in general – just the ones with five legs.”

Philosophy has grappled with the topic of war for centuries. It cannot directly answer the question of why wars happen, however, since that is a question about the causes of empirical events that other disciplines are better placed to answer. “But philosophy can help us think about things,” Surber says. Even today, her field is still preoccupied with much the same question as in the Middle Ages: when is a war just?

When it comes to specific wars, such as the war in Ukraine or the Iran war, some philosophers – including Surber – deliberately withhold judgment. “Just determining the fair punishment for a single murder often takes the justice system several years,” she says. “You can’t expect philosophy to casually settle the question of whether it is permissible to kill 10,000 people.”

In theory, though, the discipline has an answer ready. Philosophy names seven conditions that must be met for a war to be just. These include: there must be a just cause for war, such as an aggressive invasion or genocide. War may be used only as a last resort. There must be a realistic chance of achieving the goal of the war. The suffering caused must not outweigh the injustice being fought.

However, this wording leaves plenty of room for differing interpretations. “The only war that most ethicists agree meets every criterion – in other words, a truly just war – was the one against Hitler,” Surber says. That forces philosophy to confront a hard question, she continues: can a just war exist in the real world, or does it ultimately only work on paper?

The moral responsibility of soldiers is another point of debate. Revisionist theories of just war, popular in philosophy since the 1990s, treat soldiers as rational agents. Their verdict: only soldiers fighting a just war, usually the defenders, may kill.

“In practice, that would make every Russian soldier a murderer. I think that claim goes too far,” Surber says. “Can every soldier judge whether his war is just, especially when his training conditions him to think it is?” Soldiers’ actions, she argues, cannot be directly compared with the violence used by civilians, for example in self-defense situations.

Surber hopes her work will bring philosophy a little closer to reality. “We have to make very precise, neutral and honest observations before we pass moral judgment on lots of other people,” she says. In a recent essay, she probes the extent to which soldiers can be said to act with intent at all when they kill.

This led her to a bigger idea that she hasn’t been able to shake: “I believe intent, or intentional action, ultimately has a great deal to do with our ability to think. Some philosophers would put it this way: We act for reasons. I believe that this capacity for reflection is in tension with the use of violence.” Surber would like to develop this thesis in a book project.

Frederick the Great of Prussia probably did not grapple with these moral questions when he invaded Saxony in 1756, three years after issuing his generals a secret manual on handling soldiers. His actions triggered the Seven Years’ War against the great powers Austria, Russia and France. Prussia, once a provincial state, emerged from it as a major European power. Whether the beer and schnapps Frederick lavished on his men played a part is not documented.