In the fall of 2010, I packed my clothes into a duffel bag and moved from Cape Town to California. I had been awarded a year-long fellowship to report on the impact of violence and trauma on the mental health of the residents of inner city Oakland — a city in which I had never set foot and about which I knew virtually nothing. Upon arrival I was given the rather officious title of "Violence Reporting Fellow" at the Oakland Tribune.

I hadn't lived in America, my home country, for more than twelve years. I’d been working as a foreign correspondent for Newsweek, mostly in conflict zones of one sort or another. I’d spent three years in Iraq, another year in Afghanistan, four in Africa and a few more in Latin America. I had seen my fair share of war and was, I thought, intimately familiar with its ability to devastate communities. I also had a personal interest in the subject matter: after the war in Iraq, I and many other correspondents and friends had struggled, to varying degrees, with the effects of post traumatic stress disorder. I thought I could perhaps bring a measure of understanding to a beat that focused almost exclusively on just that.

The challenge was to translate the experience of reporting on large-scale wars in foreign countries, among people from vastly different cultural, linguistic and historical backgrounds, into a lens through which I could view my own people. I've been doing so for more than two years now. In that time my ideas about trauma, conflict and mental health have changed dramatically, in ways I could hardly have imagined at the outset.

Having so recently left Iraq, from where American soldiers were returning with PTSD, I was astonished to learn that children in the roughest parts of Oakland were also registering high rates of PTSD. In fact, some studies showed that the rates were at least as high as those of recent veterans. I wanted to know why the rates were so high. And why were children affected?

The reporting that flowed from those questions led to my learning of "toxic stress", a term psychologists use to refer to chronic exposure to stressful events. The events that US soldiers and Oakland residents are exposed to are very different. Soldiers often witness extreme violence in intense bursts; many residents of Oakland had been coping with violence — gangs, drug shootouts, drive-bys — for years or even decades. But in both cases the stress has the same toxic effects on their minds and bodies.

This made me rethink many of the scenes I had witnessed covering wars and insurgencies. In the spring of 2009, for instance, I traveled to Juba, the capital of the breakaway nation of South Sudan. I was working on a story about the hunt for Joseph Kony, the leader of the Lord's Resistance Army, a violent rebel group that has been active across East Africa for more than 30 years. One of the signature traits of the LRA's gruesome campaign is the recruitment of child soldiers, many of whom are stolen from their families in blood-soaked night-time ambushes. Kony's army often forces the children they kidnap to kill their own families, ensuring that the kids are too traumatized and guilt-ridden to contemplate returning home. Child soldiers have also been forced to engage in cannibalism, often of people they've been forced to kill and, in at least a few reported cases, of their own family members. One can hardly think of a more traumatic experience.

I met one of these children when I was in Juba. His name was George and he had only recently escaped from Kony's army. A refugee group in had taken him in. Soon after he would be shipped back to Uganda, his home, where he would receive intensive trauma therapy. I sat down with George in the shelter and spoke to him with the aid of a translator. He was thin, almost gaunt. His movements were slow and his eyes were deadened — so much so that I wondered whether he would be able to talk to me at all. An aid worker said that he had been sedated.

George was sixteen at the time. He told me that he had killed many people, adults and children. He said that he had eaten parts of people, and that others had done the same. George was eating a bowl of pea-green soup as he related these events to me. At the end of our conversation, I asked him what he thought should happen to Joseph Kony, should the LRA leader ever be captured. "He should be killed," George replied matter-of-factly. "And then he should be eaten."

After I arrived in Oakland, I began to spend time with young people who had been immersed in violence from an early age. One of these was a young man called James, who admitted to me that he was a criminal. He said he had been one since he was a little boy, when his aunt would ask him to break into people's houses. He had been a pimp and a drug dealer. He told me he regularly robbed people at gunpoint. One day in 2010, he had found himself on the other end of a gun. A rival gang member chased him down, shot him in the back and tried to kill him. The only reason James was alive, he said, was that his assailant ran out of bullets. James was partially paralyzed when I met him, living far from Oakland and struggling to figure out the rest of his life.

The experiences of James and George differ greatly, but the consequences were very similar. Both were very traumatized, volatile and agitated. James, who was 20, said he didn't expect to live past the age of 25. The more I reported in Oakland, the more I found this to be the case with young people. George, meanwhile, had very little in the way of expectations at all. At his home in Uganda, there were hundreds, perhaps thousands, of kids who had gone through many of the same experiences he had. They, like the youth in Oakland, would struggle for years to come to terms with their trauma.

The trauma in the lives of these distressed populations finds its most brutal expression in the brain. Whether they're in Uganda, Iraq or Oakland, a person’s brain reacts to trauma in much the same way. Cortisol levels rise and their stress response systems go haywire. They make poor choices as a result. They self-medicate, further changing their brain chemistry. Some of this science was the subject of "Ghost in the Cell”, a recent piece I wrote for MATTER. The story describes how the chemical signature of violence and stress can become embedded in the brain — and possibly even be passed along to the next generation.

This is troubling but also very exciting science, and it is bound to change the way we think about how to intervene more effectively in the lives of people like James, in Oakland, or George, in Uganda.

The time I’ve spent in Oakland has opened my eyes to the extent of trauma in many inner city neighborhoods, both in severity and scope. But because we live in a wealthy country, it is tempting to think that people in difficult situations can simply bounce back in ways that other people, like George, cannot. This is a mistake. From the outside, the victims of urban violence in America may look okay. After all, they have iPhones and cars and nice clothes. But traumatic wounds are often invisible, located in the body’s neuronal circuitry, adrenal glands, glucocorticoid receptors and epigenetic pathways. The wounds of war on a battlefield are severe, but there is a war going on in America’s inner cities as well, and there are just as many casualties. I think we need to pay more attention to them.

For more on the connection between biology, violence and the streets of Oakland, see “Ghost in the Cell”, published this month by MATTER.