Combat and post-traumatic stress disorders in military veterans are not new, though the conditions have been called many other names throughout the years: “insanity” and “melancholia” during the Civil War, “shell-shock” during World War I and “combat fatigue” during World War II.

Top military leaders are now addressing the lingering effects of post-traumatic stress disorder, (PTSD) which were ignored for many years because they were seen as a sign of weakness. Last week, Gen. George Casey, the chief of staff of the U.S. Army, called PTSD “the defining military health issue of our era.”

Consider that statement alongside the much-recounted story from World War II, when Gen. George S. Patton infamously slapped a solider suffering from “nervous exhaustion” in a military hospital and ordered him back to the front.

That story, and others from wars stretching from the Civil War to the current battles in Afghanistan and Iraq are chronicled in a new HBO documentary, Wartorn 1861-2010, which combines footage, interviews and documents to examine the effects of PTSD on soldiers returning from the battlefield.

Directors Jon Alpert and Ellen Goosenberg Kent joined Fresh Air’s Terry Gross for a discussion about the film, which features interviews with veterans of World War II, the Vietnam War, Operation Desert Storm and Operation Iraqi Freedom.

One difficulty the two directors encountered, Kent says, was trying to find information about combat trauma in the Civil War. Unlike today, there was little documentation of combat trauma. instead, the filmmakers sifted through pension files to learn what soldiers’ families said about them when they came home from the war.

“Those were really the only recognition that there would be something wrong with [the soldiers],” Kent says. “Their family would attempt to get a pension because their breadwinner came home from the war and wasn’t able to function psychologically. going through these really unsexy legal documents led to individual stories from Civil War servicemen.”

One solider, Angelo Crapsey, wrote letters and kept a diary during his time in the service, allowing Goosenberg and Alpert to chart changes in his mental status. during his initial letters to family and friends in 1861, Crapsey sounds hopeful and confident. But by 1863, the tone of Crapsey’s letters had changed.

“His father gets a call from the hospital that he needs to come pick him up and visit him because he’s declining physically,” Kent says. “But when Crapsey [eventually comes home,] everyone notices he’s a completely different person than the one who left. He’s paranoid, he’s in and out of reality. he feels hated. he feels like he’s a killer. and he attempts suicide several times and doesn’t complete the suicide.”

On a hunting trip several weeks later, Crapsey shot and killed himself. In order to collect his pension money, his family had to prove that he killed himself as a result of being at war. The incident, Kent says, parallels what many veterans face today when struggling to prove they have PTSD in order to obtain health benefits.

“It’s really what the essence of the film is,” Kent says. “If you have any doubt that PTSD is a real thing or you wonder what causes it or you think PTSD happens because the war is good or it’s bad or you come home a hero or villain, it’s really irrelevant. What’s really relevant is that the experience of war — and experiencing man’s inhumanity to man — causes psychological damage. and that’s really what we wanted to show.”

It was not until World War I and World War II, Alpert says, that military officials began to realize that soldiers were coming home with psychological ailments that weren’t predicted.

“They didn’t know what to do about it,” he says. “They didn’t know what to call it [and] they didn’t understand completely why people were suffering like this.”

And military veterans stayed quiet about the after-effects that lingered.

“Having battle fatigue was something nobody wanted to own up to,” Kent says. “Because you were a coward. you were a malingerer. … it was absolutely not okay to be unwell psychologically when you came home. and when you came home, you were expected to be a hero and you were expected to be somebody who marched forward in life. nobody wanted to talk about it and the VA, as one of the veterans described in the film, was absolutely overwhelmed.”

Some World War II veterans were not diagnosed with PTSD until decades later, when the symptoms of PTSD were finally recognized as a real psychological illness.

“Some [World War II veterans] were beginning to enter retirement age and they were starting to re-experience symptoms,” says Kent. “And so they were kicked back to the VA and all of a sudden the VA said ‘Maybe you have PTSD’ and they were, in some degree, incredibly grateful for that diagnosis. They finally understood what the hell was wrong.”

Today’s military is trying to address the mental disorders and high suicide rates that have climbed since 2001, Alpert says.

“The military’s made it easier to get diagnosed with PTSD. you don’t have to prove that it was a specific traumatic incident. it could be the cumulative effects of being in a war zone,” Alpert says. “That also means that many, many people are in need of treatment and the cost of treatment that society’s going to bear is really going to be quite substantial.”

Alpert explains that the military is trying to change the perception of PTSD from the top down.

“The generals — for the first time — are talking about this. you don’t have somebody like General Patton” [any more] he says. “They’re saying the right things. But this is something that’s very difficult to deal with in a martial atmosphere, where you’re supposed to be tough, you’re supposed to be resilient and things aren’t supposed to affect you like this. But they’re saying ‘It’s okay to be wounded. It’s okay to be psychologically damaged. We’re going to try to treat you and send you back.’”

Jon Alpert and Ellen Goosenberg Kent previously worked together on the HBO documentary Addiction. Alpert has made films for NBC, PBS and HBO and received 15 Emmy Awards and three DuPont-Columbia Awards. Kent has received three Primetime Emmy Awards, a Peabody Award and other honors for her work on films for HBO, A&E and children’s television.