Wars are decided by governments but fought by individuals. What is the moral position of the person holding the rifle? Is a soldier fighting for an aggressor a wrongdoer, a victim, or simply a soldier like any other?
The moral equality of combatants
The traditional answer, and the one built into the laws of war, is that soldiers stand on equal terms. Walzer gave it its best-known modern defense. On the moral equality of combatants, soldiers on both sides have the same right to fight, whatever the justice of their cause. The crime of aggression belongs to the leaders who start a war; the soldiers who fight it are judged only by how they fight.
Why accept this? Defenders argue that soldiers are often conscripted, misled and unable to judge their cause. A nineteen-year-old drafted into an army has no access to the intelligence reports and diplomatic cables that would let him decide whether the war is just, and his government is working hard to convince him that it is. The idea is old. In 1539 the Spanish theologian Francisco de Vitoria, lecturing at Salamanca on the law of war, held that a war could be truly just on only one side, but that soldiers on the unjust side might be excused by invincible ignorance, a lack of knowledge that they could not reasonably have overcome.
The equality principle also does practical work. If soldiers on the unjust side were treated as criminals merely for fighting, they would have no reason to obey the rules, to take prisoners or to surrender.
The challenge
Since the 1990s the philosopher Jeff McMahan has led a powerful attack on this view, set out most fully in his 2009 book Killing in War. He asks us to consider a bank robber who shoots a police officer in self-defense after the officer fires at him. Nobody thinks the robber and the officer are moral equals. Why, then, should a soldier invading another country have the same right to kill as the soldier defending it? McMahan argues that those fighting for an unjust cause lack a moral right to kill. They may be excused, as Vitoria said, but excuse is not the same as justification.
McMahan does not, however, want to rewrite the law of war to match. Precisely because each side believes it is in the right, and because no impartial court decides which side is just while the fighting continues, McMahan holds that the law should still treat both sides' soldiers alike. The result is a gap between the deep morality of war and its law, a gap that many philosophers now accept as unavoidable.
Surrender, prisoners and refusal
Whatever their cause, soldiers who stop fighting gain protection. The Hague rules of 1907 forbid declaring that no quarter will be given, and the Third Geneva Convention of 1949 sets out the treatment owed to prisoners of war, who must be housed, fed and protected from violence and public curiosity. Interrogation is limited too: a prisoner of war is required to give only name, rank, date of birth and serial number.
Some people refuse to fight at all. Many countries recognize conscientious objectors who reject all war. Fewer accept selective objection, the refusal to fight in one particular war believed to be unjust. In Gillette v. United States (1971), the Supreme Court upheld denying exemption to objectors to one particular war. Critics note the irony: just war thinking holds that some wars are unjust, yet the law makes no room for a citizen who reaches that conclusion.
Finally, soldiers bear what they have done. The psychiatrist Jonathan Shay, working with American veterans of the Vietnam War, helped popularize the term moral injury: lasting harm from doing, failing to prevent or witnessing acts that violate one's own moral code. Moral injury differs from fear-based trauma; its marks are guilt, shame and a broken trust in leaders or in oneself.
Worked example: My Lai and Hugh Thompson
On 16 March 1968, American soldiers of Charlie Company entered the hamlet of My Lai in South Vietnam, expecting to find enemy fighters. They found none, yet over the following hours they killed somewhere between about 350 and 500 unarmed villagers, most of them women, children and old men. Above them, a helicopter pilot, Warrant Officer Hugh Thompson Jr., saw what was happening. With his crew, Glenn Andreotta and Lawrence Colburn, he landed between the soldiers and a group of fleeing villagers, confronted the officer in charge, and arranged to fly the villagers to safety. Andreotta pulled a small child alive from a ditch full of bodies.
The massacre was covered up for more than a year until a former soldier's letters and a journalist's reporting forced an inquiry. Of the soldiers charged, only Lieutenant William Calley was convicted, and he served about three and a half years, mostly under house arrest. Thompson and his crew received the Soldier's Medal only in 1998. The case maps the level's ideas. Moral equality never covered killing villagers. Superior orders could not excuse it. And Thompson showed that even inside an army at war, a soldier remains a moral agent who can refuse, and resist, a crime.