Recently I saw the film "In the Valley of Elah", with Tommy Lee Jones, who has been nominated for an Academy Awards prize for the film, and Charlize Theron as the main-characters.
The plot evolves around the war in Iraq. Jones's character, Hank Deerfield, is informed that his son has gone missing from the army, and becomes suspicious. It turns out that his son had been killed, his body burnt, cut into small pieces and dumped at the side of a road close to the military base. After much drama it is discovered that the son was killed by his friends from the army, for no reason at all. They had been out and drank a bit too much and there was an argument. Suddenly one of his friends attacked him with a knife and stabbed him.
This shows what can happen to people who have been in conflicts, such as in Iraq and Afghanistan. The friends in the film had no intention of harming each others, it just "happened". Being in such conflicts changes people's minds and when you return, it's hard to be the same person. Post-traumatic stress disorder and depressions are common, and thing you have seen or done in those conflicts can haunt you for decades.