During World War II, military psychiatrists accepted that the phenomenon of combat stress existed, but had not learned to prevent or treat it. A whopping 23% of American soldiers evacuated from battle suffered from psychiatric, not physical, wounds. At one point during the war, the number of Americans discharged for psychiatric reasons exceeded the number of new recruits.

Since World War II, the rate of PTSD among American soldiers has dropped off steeply-in part due to better prevention and treatment, in part due to technology which gives soldiers more distance from the battlefield. In the Korean War, psychiatric evacuations accounted for just 10% of all medical evacuations. In Vietnam, the figure dropped to 7%, and during the first Gulf War, the number fell to less than 1%.