The mass destruction and relentless bombings of WWI pushed troops to the limit of their senses. The human mind can only see so much death and destruction before it cracks and when it does, the result is post-traumatic stress disorder or "shell shock." Many commanders, not understanding the gravity of shell shock, had soldiers afflicted with shell shock executed for treason and refusal to obey orders. Today, we take great care to help our soldiers deal with the psychological stresses of combat. Yet another lesson from World War I.