The military believes this has to do with how recruits are selected and trained, as well as the great deal of attention that is paid to troops morale over there. PTSD, formerly known as Combat Fatigue, was first widely noted in the late 19th century, after the American Civil War. That war was one of the first to expose large numbers of troops to extended periods of combat stress. This had long term effect on many soldiers. This was publicized after the war by the newly invented mass media. The PTSD symptoms, as reported in the press over 150 years ago, have not changed. At the time, veterans were diagnosed as suffering from "Irritable Heart" (a popular description, back then, for stress related mental problems.) Symptoms noted included fatigue, shortness of palpitations, headache, excessive sweating, dizziness, disturbed sleep, fainting and flashbacks to traumatic combat situations. In World War I, the condition was called Shell Shock, and the symptoms were the same, although there was more attention paid to vets who jumped and got very nervous when they heard loud noises. During World War II and Korea, the condition was called Combat Stress Reaction. Same symptoms. During Vietnam, the term " Post-Traumatic Stress Syndrome" became popular, until it evolved into what we currently regard as PTSD. Actually, if you comb through military writings for the last few thousand years, you will note that PTSD has always existed. Too much combat "leaves a mark on a man" as the ancients were wont to note. But, the condition could always be faked or, more commonly, as many veterans preferred, hidden. Whatever the case, PTSD is real.
Medical research is getting close to being able to diagnose PTSD with a great deal of certainty, whether the victim wants to admit to admit having it or not. For example, it's now possible, via a blood test, to determine who is most vulnerable to the psychological aftereffects of combat. This makes it possible to keep people out of combat units, who are likely to be most vulnerable to PTSD. This kind of screening, using cruder tools, has been done for a long time. You don't want people with you in combat, who are more prone to get quickly traumatized by it. Again, the old saying, "he doesn't have the nerves for it."
In combat, someone having a mental breakdown can be dangerous for those around him. This is one of the reasons for stressful training. It both gets troops accustomed to working under stress, and also identifies those who can't handle. There are plenty of less stressful, and safer, jobs for these guys. Only about ten percent of the troops in the army have combat jobs, and even in a place like Iraq, only about a third of the troops are exposed to any kind of combat.
Nearly 140,000 female American troops have served in Iraq and Afghanistan since September 11, 2001. More so than men, the women served in non-combat jobs. For example, while about one in 200 men in Iraq were killed in combat, only about one in a thousand women died there. But women still faced a lot of the same stress that men did. However, when they returned, it was found that women did not suffer from PTSD (Post-Traumatic Stress Disorder) to the same degree as men. PTSD is a mental condition, and difficult to diagnose with certainty (unlike, say, a missing limb or eye). Women have always been more willing to seek medical care than men, and in the general population, women are diagnosed with stress related conditions twice as often as men. But not the women who have served in a combat zone.