The enemy fighters were often young men raised alongside poppy fields in small farms set up like latticework along the river. They must have been too young and too isolated to understand anything outside of their section of the valley, never mind something global like the 9/11 attacks. These villagers fought us because that’s what they always did when foreigners came to their village. Perhaps they just wanted to be left alone.

The more I thought about the enemy, the harder it was to view them as evil or subhuman. But killing requires a motivation, so the concept of self-defense becomes the defining principle of target attractiveness. If someone is shooting at me, I have a right to fire back. But this is a legal justification, not a moral one. The comic Louis C.K. brilliantly pointed out this absurdity: “Maybe if you pick up a gun and go to another country and you get shot, it’s not that weird. Maybe if you get shot by the dude you were just shooting at, it’s a tiny bit your fault.”

My worst fear before deploying was what, in training, we called “good shoot, bad result.” But there is no way in the chaos and uncertainty of war to make the right decision all the time. On one occasion, the Taliban had been shooting at us and we thought two men approaching in the distance were armed and intended to kill us. We warned them off, but it did no good. They continued to approach, and so my Marines fired. What possible reason could two men have to approach a squad of armed Marines in a firefight? When it was over and the two men lay dead we saw that they were unarmed, just two men trying to go home, who never made it.

On most occasions, when ordnance would destroy the enemy or a sniper would kill a Taliban fighter, we would engage in the professional congratulations of a job well done like businessmen after a successful client meeting. Nothing of the sort happened after killing a civilian. And in this absence of group absolution, I saw for the first time how critical it actually was for my soul and my sanity.

Nobody ever talked about the accidental killing. There was paperwork, a brief investigation and silence. You can’t tell someone who has killed an innocent person that he did the right thing even if he followed all the proper procedures before shooting.

When I returned home this group absolution was supposed to take the form of a welcoming society, unlike the one Vietnam veterans returned to. But the only affirmation of my actions came through the ubiquitous “Thank you for your service.” Beyond that, nobody wanted to, or wants to, talk about what occurred overseas.

IV.

The first Marine to be grievously injured on our deployment was shot in the neck during a firefight exactly nine years and nine days after the Sept. 11 attacks. He was a 19-year-old from Mississippi on his first tour after enlisting straight out of high school. Under enemy fire, the Navy corpsman and Marines in his squad gave him medical care as the evacuation helicopter raced to get him to the field hospital in the critical “golden hour.”