This is true, disease killed huge numbers of troops in the Civil War. A majority of the soldiers were farm boys who lived in isolation, and when they were all mixed up with other farm boys and city boys, many of them immigrants, everyone swapped germs and they died by the thousands. The years during the Civil War were unusually cold ones, and a lot of soldiers froze to death as well.
PBS recently reran Ken Burn's Civil War documentary,and the American Experience series also showed some excellent bios of both Grant and Lee.
One of my 2nd great grandfathers was a surgeon with an Illinois regiment, another was a surgeon with John Bell Hood's Texas Brigade. My father was born in 1902 in North Texas, he said that there was always a bunch of old whiskerandos hanging out and whittling and trading war stories at the hardware store. My father heard a number of these when he was young, and asked his grandfather (the one with the Texas Brigade) about the war, and the old man said, "Son, I have spent the last 45 years trying to forget that war, and you don't want to hear what i have had to see."
He spent the war amputating arms and legs and trying to keep the wounded from dying. The Union grandfather moved to Texas after the war because of some land he had inherited, but he died before my father could talk.
