Thousands of Iraq and Afghanistan veterans are joining over 100,000 existing veterans from past wars who are living on the streets and in shelters. Veteran's aid has been a major focus of non-profit organizations since the wars in Iraq and Afghanistan began well over a decade ago. In World War I, it was known as shell shock, and in earlier centuries terms such as soldier's heart, nostalgia, and mental exhaustion were often used. In World War II, the problem went by the term combat fatigue. Post-Traumatic Stress Disorder (PTSD) is a disease or injury affecting human identity in the aftermath of a traumatic event or series of events that cannot be fully comprehended or absorbed by the human mind. Reactions to traumatic experiences vary from person to person. PTSD can result from Military Sexual Trauma (MST) including sexual harassment, assault, and rape.