Post-Traumatic stress disorder is a large-scale problem. The disorder starts with a trauma, and gradually develops. It causes massive social and emotional dysfunction. Science shows that PTSD also creates biochemical and neurological changes, such as that the Hippocampus becomes 20% smaller. Genetic disposition might also be related to the risk of getting PTSD. Today, it's estimated that approximately 8% of the population have PTSD
PTSD is especially associated with wars or conflicts. The disorder is today a major issue, as about 20% of US troops in Iraq and Afghanistan suffer from PTSD or depressions. However, PTSD has always been a consequence of warfare and is well-known through history. It has many different names, and has seemingly been "rediscovered" several times. It has been called post-Vietnam syndrome, K-Z syndrome, Shell Shock etc. and the first historical reference to a disorder similar to the modern Post-Traumatic Stress Disorder, was after the battle of Marathon in 490 BC and written by the Greek historian Herodotus.
Updates might follow, but now I'm too sleepy to continue. ^_^