I've been researching my family tree and found an ancestor who fought in the Arkansas 1st during the civil war. He was just a lowly private so there are no books written about my ancestor directly, but my understanding right now is that when a southerner wanted to oppose the confederacy, he would either flee north to join a regiment or else go into hiding from the confederate press-gangs. In the case of Arkansas, they were chased into the hills and called "Mountain Feds". Later, a Union Colonel came south and raised the Arkansas 1st to fight against the confederacy. So far all of my reading has been online (ancestry.com and wikipedia) and I want to learn more. I'm particularly interested in:

What were some reasons that men from the south might join the union?

What was life like for "Mountain Feds" or people who stayed in the south while opposing the confederacy?

How were southerners who fought for the north treated when they returned home after the war?

edit: super extra bonus points if you know of a good book about the arkansas 1st or of a
journal by someone in a similar situation as my grandfather.