Having just finished reading it, I highly recommend Noel C. Fisher's Book "War at Every Door: Partisan Politics and Guerrilla Violence in East Tennessee, 1960-1869" (The University of North Carolina Press, 1997).This book was the 1997 winner of the Peter Seaborg Award for Civil War non-fiction.
Most of my research has focused on northwest Alabama, and I was struck by the many similarities between what occurred in east Tennessee and in NW Alabama. This was even down to a man known as "The Red Fox" guiding men to Union lines in E.TN compared to the "The Black Fox" in NW AL.
I have contacted Dr. Fisher and told him about this board, and I strongly suspect that he would be pleased to respond to questions about Unionism in east Tennessee and elsewhere.
I'll start: Of the places in the south where Unionism was prevalent, what are some characteristics of east Tennessee that made the situation there unique?