Commentary: Why do so many veterans kill themselves?

Why do so many soldiers continue to take their own lives at a higher rate than their civilian counterparts, whether young or old? I've spent a lot of time stewing about this over the past few days.

It began Monday morning, when I got a note from a vet in a very dark place and contemplating the act. He'd served in Vietnam. His risk of suicide is about 22 percent higher than that of his nonveteran peers, according to a report last year from the Department of Veterans Affairs.

That afternoon, I learned that an Army captain who had been featured a while back in my old "Best Defense" column on the Foreign Policy website had gone out in the middle of the night and sat on railroad tracks near Fort Carson, Colorado, and apparently let a train run over him. He was still in the military but may have been thinking of leaving. People getting out are at the highest risk in the year after they leave - about 1½ to two times as likely to kill themselves as those still on active duty.

A friend of his wrote to me, "He was always a high-performing and intelligent guy. He had deployed to Afghanistan with 10th Mountain, then to Kuwait with 4th ID prior to Atlantic Resolve where it looks like you met him. He was on deck to teach Military Science at West Point. He had a wife and daughter. Nothing about his death makes sense. The only indicator I had that he was unhappy was his deep frustrations with the conventional military, the high op tempo for support roles and exercises, and the impact on his family."

Last month, the commander of the Marine 4th Reconnaissance Battalion was found dead in his home. He also had deployed several times to Iraq and Afghanistan.

Also recently, I read that a retired major who had served in military intelligence in Iraq had killed himself and his wife.

The suicide rate for veterans has gone up 35 percent since 2001, in part because of increases in post-9/11 veterans killing themselves.

I know what I am seeing around me is anecdotal. But it just doesn't feel right to me. What is going on here?

Here are four possibilities, specific to the conditions of our recent war:

A lost war: My initial thought was that perhaps people are feeling empty and lost as the Middle Eastern war winds down and we don't have a lot to show for it, besides Iran being more powerful than ever. But a friend who did several tours in Vietnam said he also knew that feeling but didn't see any rash of suicides in the '70s among his former comrades.

Death by rotation: Another theory is that everyone is born with just so much to give and that repeated deployments drain that reserve, without replenishment. At some point, a person might just decide they can't do this anymore, that this is too painful and look for the fastest exit.

Brain injury: A third theory, related to the extensive use of roadside bombs in the Middle East, suggests that the human brain can, at best, withstand only one or two nearby explosions and cannot heal the deep damage inflicted by repeated blasts.

More to come: Or is it that depressed vets are responding to the whiff of another possible war on the horizon, with North Korea?

Whether it is one of these, or a combination, or something else, it worries me deeply.

Thomas E. Ricks is the author of five books about the U.S. military. He writes "The Long March"column for Task & Purpose, a veteran-oriented website.