Except for sociopaths, one of the most traumatic events that a soldier can experience is witnessing harm to others—even to the enemy. In a survey carried out after the first Gulf War by David Marlowe, an anthropologist who later worked for the US Department of Defense, combat veterans reported that killing an enemy soldier, or even witnessing one getting killed, was more distressing than being wounded themselves. But the very worst experience, by far, was having a friend die. In war after war, army after army, losing a buddy is considered the most devastating thing that can possibly happen. It is far more disturbing than experiencing mortal danger oneself and often serves as a trigger for psychological breakdown on the battlefield or later in life.
Still, most soldiers go through that and other terrible experiences and don’t wind up with long-term trauma. Multiple studies, including a 2007 analysis from the Institute of Medicine and the National Research Council, found that a person’s chance of getting chronic PTSD is in great part a function of their experiences before going to war. Statistically, the 20 percent of people who fail to overcome trauma tend to be those who are already burdened by psychological issues, either because they inherited them or because they suffered abuse as children. If you fought in Vietnam and your twin brother did not—but he suffers from a psychiatric disorder such as schizophrenia—you are statistically more likely to get PTSD. If you experienced the death of a loved one, or if you weren’t held enough as a child, you are up to seven times more likely to develop the kinds of anxiety disorders that contribute to PTSD. According to a 2000 study in the Journal of Consulting and Clinical Psychology, if you have an educational deficit, if you are female, if you have a low IQ, or if you were abused as a child, you are also at an elevated risk of developing PTSD. (The elevated risk for women is due to their greater likelihood of getting PTSD after a physical assault. For other forms of trauma, men and women are fairly equal.) These risk factors are nearly as predictive of PTSD as the severity of the trauma itself.
Suicide is often seen as an extreme expression of PTSD, but researchers have not yet found any relationship between suicide and combat. Combat veterans are, statistically, no more likely to kill themselves than veterans who were never under fire. The much-discussed estimate of twenty-two vets a day committing suicide in the United States is deceptive: it was only in 2008 that—for the first time in decades—the suicide rate among veterans surpassed the civilian rate in America, and though each death is enormously tragic, the majority of those veterans were over the age of fifty. Many were Vietnam vets and, generally speaking, the more time that passes after a trauma, the less likely a suicide is to have anything to do with it. Among younger vets, deployment to Iraq or Afghanistan actually lowers the risk of suicide, because soldiers with obvious mental health issues are not deployed with their units.
Further confusing the issue, voluntary service has resulted in a military population that has a disproportionate number of young people with a history of sexual abuse. One theory for this holds that military service is an easy way for young people to get out of their home, and so the military will disproportionally draw recruits from troubled families. According to a 2014 study in the American Medical Association’s JAMA Psychiatry, men with military service are now twice as likely to report sexual assault during their childhood as men who never served. This was not true during the draft. Sexual abuse is a well-known predictor of depression and other mental health issues, and the military suicide rate may in part be a result of that.
Killing seems to traumatize people regardless of the danger they’re in or the perceived righteousness of their cause. Pilots of unmanned drones, who watch their missiles kill human beings by remote camera, have been calculated to have the same PTSD rates as pilots who fly actual combat missions in war zones. And even among regular infantry, danger and trauma are not necessarily connected. During the 1973 Yom Kippur War, when Israel was simultaneously invaded by Egypt and Syria, rear-base troops had psychological breakdowns at three times the rate of elite frontline troops, relative to the casualties they suffered. (In other words, rear-base troops had fairly light casualties but suffered a disproportionately high level of psychiatric breakdowns.) Similarly, more than 80 percent of psychiatric casualties in the US Army’s VII Corps came from support units that took almost no incoming fire during the air campaign of the first Gulf War.