I hope Ageod doesn't mind me posting the link to Frank Hunter's old American Civil War game "From Sumter to Appomattox". I bought it when it first came out in 1996 and have played it numerous times. Now Hunter has released the code for free and it can be downloaded at the below website.
Unfortunately there is no sound with this version and the graphics are basic, but the strategy play is pretty solid. I still play this version when I want my ACW strategy fix.
Frank Hunter's "American Civil War:From Sumter to Appomattox"