First answer: opiate addiction
Second answer: Opiate addiction is vague, not to mention that it doesn't state the historical significance of "soldier's disease."
Morphine, the active agent in the opium poppy, was isolated in 1806, and was used widely during and after the Civil war, its administration greatly facilitated by the introduction of the hypodermic needle in the late 1840s. The widespread use of morphine during the Civil War is generally considered responsible for large numbers of soldiers developing the "solider's disease" - which was morphine addiction.
Disease. Remember this was before vaccinations against disease were created. More soldiers died from disease that died from bullets. Besides unsanitary living conditions, add bad food and bad water.
Disease
There were 1,600 British soldiers that were killed in action during the War of 1812. 3,321 soldiers perished because of disease.
Disease
close quarters
close quarters
Yes, more died from disease than from battlefield trauma.
2,000,000
Certainly - but not as many as disease.
The main cause of death in the US Civil War was disease because of the unsanitary conditions in hospitals used to care for wounded soldiers. One of the greatest killers was Dysentery, a disease that killed over 45,000 Union soldiers and 50,000 Confederate soldiers. It is estimated that two thirds of all deaths among US Civil War soldiers were due to various diseases.
In The Killer Angels by Michael Shaara, it was the severe diarrhea that soldiers got from eating too much fresh fruit.
More than 50% of the soldiers who died in the Civil War died of disease or complications from their wounds.