By Richard Allen Greene
The physical wounds left by the war in Iraq are all too easy to see. But survivors of war are often left with mental scars as well, whether they are soldiers or civilians, victors or vanquished. In this five-part series, BBC News explores what happens when the fighting stops - but the trauma continues.
World War I veterans called it shell shock.
The World War II generation talked about soldiers "going psycho".
Today it is called post-traumatic stress disorder (PTSD) - psychological trauma caused by bad experiences.
Victims often find themselves having nightmares or being unable to sleep. In many cases, they have intrusive flashbacks to the events that caused the trauma.
Since the US-led invasion of Iraq in 2003, tens of thousands of US soldiers - and hundreds from the UK - have been diagnosed with PTSD and related problems such as depression.
It is much harder to get a picture of the situation in Iraq because of cultural differences and the relative lack of psychological services there.
But experts and eyewitnesses agree that the invasion and insurgency are certain to have caused serious mental health problems for many.
Dr Jonathan Shay, a US psychiatrist who has worked with Vietnam veterans for many years, says combat stress is an age-old problem - certainly one known to the ancient Greeks.
In his book Odysseus in America, he argues that the Homeric hero was a severe combat stress case - a loner and deceiver who had murderous rages.
"Combat stress is as old as the human species," he says - and, in a way, a very normal phenomenon.
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"It is an absolutely valid adaptation to survive in a horrific situation. In war, people really are trying to kill you. You are surrounded by enemies and have to be prepared to kill instantly to survive."
Soldiers - and civilians caught up in war - become hyper-vigilant, unnaturally alert and focused.
And combat can have a devastating effect on a person's emotional health.
"We shut down all emotions that do not serve survival - grief, sweetness, fear," Dr Shay says.
But one emotion may remain switched on, he adds: anger.
"So a veteran comes home with all emotions shut down except for anger. Guess what this does in the family, in the workplace. It's a problem," he says.
Some cope with it by withdrawing from society in one way or another.
"There are numerous examples where a veteran will severely limit his life, isolating himself to protect us," Dr Shay says.
"They will tell you: 'If I go out in public, I know I'm going to meet some jerk who's going to cross me and I'll do something and spend the rest of my life in jail.' Many truly don't want to hurt other people."
Those are the extreme cases, of course. Only a minority of soldiers - even those who see combat - experience PTSD.
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One recent UK study of Iraq veterans even suggested that a successful military deployment could be beneficial for a soldier's mental health.
But Jamie Hacker-Hughes, the author of that study, emphasised that his subjects were "professional soldiers who went as a unit, did exactly what they were trained to do, had a successful outcome, and were there for a relatively short time".
And the sample was fairly small - 254 soldiers.
A much larger US study of veterans of the wars in Iraq and Afghanistan found up to 17% suffering PTSD, depression, or general anxiety.
And while some research has been done on the British and US soldiers who served in Iraq, there is much less data on the mental health of Iraqi soldiers or civilians on the receiving end of the war.
Leslie Carrick-Smith, a leading British expert on PTSD, says the "propensity for trauma would be the same if not greater" among Iraqis caught up in combat zones.
Baghdad has a psychiatric hospital, but it is understaffed, under-resourced and overwhelmed.
Khalid, a surgeon in Baghdad, says mental health is a low priority in post-war Iraq.
"Being operated on physically is the most important," he says. "No-one had, or has, the time to ask: 'Are you afraid? Are you stressed?'"
John Henry Parker runs Veterans and Families, a California-based organisation dedicated to supporting soldiers and their loved ones when they return from combat.
He warns that soldiers suffering from psychological trauma pose a risk to themselves, their families and society if they are not treated.
"They burn through their family and the goodwill of everyone they know, because there's no way a normal person can deal with PTSD.
"We're not trained for it. People have to part ways and it's ugly," he says.
And in the United States, tens of millions of people are affected, he says.
"There are about 25 million veterans in America.
"Multiply 25 million veterans by their spouses, their surviving parents, their aunts, uncles, cousins, sisters, brothers - that's 100 million people."
On Tuesday: How US soldiers deal with trauma.