War syndromes and their evaluation: from the U.S. Civil War to the Persian Gulf War.
Hyams, K C, Wignall, F S, Roswell, R·Annals of internal medicine·1996
Researchers reviewed historical records of illnesses that appeared in soldiers after wars, dating back to the U.S. Civil War through the Persian Gulf War. They found that across different wars and time periods, veterans reported similar symptoms like exhaustion, breathing problems, headaches, and difficulty concentrating. However, the researchers concluded that these symptoms don't appear to be one single disease, and that lack of proper comparison groups and research methods made it hard to determine what actually caused these illnesses.