War is such a constant in the American experience that most of us are all-too familiar with the names we have given its emotional consequences in the past century: shell shock; battle fatigue; operational exhaustion; and now, post-traumatic stress disorder.

But most Americans are less familiar with a related, if distinct, affliction known as moral injury, with roots in foundational religious or spiritual beliefs violated during war. And increasingly, military chaplains are on the front lines, tending to these misunderstood wounds.

Psychiatrists have used the term since the 1990s, but the concept has only recently been the subject of serious research by clinicians, some affiliated with the U.S. Department of Veterans Affairs.

“We’ve come a long way in defining moral injury, but it takes a long time to develop a tool to measure it,” said Shira Maguen, a psychologist at the San Francisco VA Medical Center who is working to develop treatment models for moral injury.

Maguen has helped the VA define an event as morally injurious if it transgresses “deeply held moral beliefs and expectations.”

Col. Thomas C. Waynick is a senior Army family life chaplain at Fort Benning, Ga., who is helping to develop training for chaplains to treat moral injury. He puts it this way: “In the course of doing what I’m called to do, what I know how to do, what I’m trained to do — I violate one of my core moral principles . . . and that can split the soul.”

Often a soldier faced with a life-or-death decision doesn’t have time to sort out right and wrong. The outcome of split-second decisions — driving past someone who needed medical help, shooting a civilian who failed to stop at a check-point — can lead to feelings of guilt and shame.

Unlike PTSD, which has roots in trauma-based fear, the trauma that leads to moral injury is most often rooted in something the person did (or didn’t do). Although the two are distinct, they can share psychological turf.

“Something terrifying happens to you, and your fear system goes haywire,” said Rita Brock, director of the Soul Repair Center at Texas Christian University’s Brite Divinity School.

“Often in the middle of being terrified, you do something you feel terrible for afterward,” Brock said. PTSD and moral injury, she said, “overlap a lot, especially in war combatants.”

Because the research on moral injury is in its infancy, there are no data yet on the number of combat veterans who suffer from it. But many who study moral injury say the destruction of internal ethical fabric as a result of combat goes back as far as Ajax in the ancient Greek epic poem “The Iliad.”

“Some of the towering figures in theology were trying to rebuild a moral system out of the ashes of war,” Brock said. “Moltmann, Barth, Tillich, Wiesel — their entire universe and moral systems had collapsed, and they were trying to build theologies adequate to live up to that.”

But modern population-centered warfare has also made it more likely that today’s combatants will find themselves in morally precarious situations.

“There are no long front-lines,” said Nancy Sherman, a philosophy professor at Georgetown University and author of “Afterwar: Healing the Moral Wounds of Our Soldiers.”

“The city or village is the war zone today,” she said. “Women and children are armed. Men are fighting without uniforms.”

At the same time, because of their proximity to civilians, U.S. combatants are subject to restrictions on the rules of engagement. “Greater troop restraint in that environment means greater risk to self,” Sherman said.

Many combat veterans see additional risks even when the guns have quieted. Because they think that reporting any psychological impact from combat can harm their careers, many troops seek out chaplains for confidential conversations.

Chaplains “are often regarded by the forces as safe,” Sherman said. “They won’t have a doctor’s appointment that shows up on their record. Chaplains are increasingly going out to forward operating bases so they can be right there for critical debriefings.”

In one sense, Waynick said, training chaplains to minister to troops suffering from moral injury is simple.

“It’s the role chaplains have always had,” he said. “Where there’s a spiritual existential crisis, no one else in the military system has the task to help with that.”

Ultimately, most moral-injury experts agree, healing mandates forgiveness of some kind. Some want God to forgive them; others learn to forgive themselves. Still others can’t forgive themselves for taking another human life, so they angle for something else.

“Nothing will be able to restore the life I took, or fix what did,” said TCU’s Brock, channeling the mind of someone suffering from moral injury. “But if I come to accept it — this is who I am — I can build life without letting this event define me. That’s a kind of forgiveness.”

— Timeline