Looking at the records of 35,000 Union Army veterans who had served between 1861 and 1865, a 2010 study found that soldiers whose military units lacked a sense of camaraderie were six times more likely to have had heart attacks or strokes by their late fifties or early sixties than counterparts from units with strong esprit de corps. “Somehow being armed with close social bonds in the extremely stressful situation of battlefield combat,” said one of the researchers, “has a protective effect that continues long after the fighting has ended.”