I have searched the web for the history of the mountain dulcimer more than once. Just now I used my Encyclopedia Britannica subscription. All I find are generalizations. I don't find any dates, newspaper references or old photographs.

They say it's Appalachian. Appalachian is a term so vague as to have almost no meaning.   

I feel that nobody can prove either way that the mtn dulcie was around or was not around by the time of the American Civil War.