The Timeline 191 series is Harry Turtledove's most sweeping Alternate History work so far: Either ten or eleven books (depending on who's counting). Set in a world where the Union failed to intercept a message (Special Order 191, hence the timeline's name) intended for a Confederate officer before Antietam, which resulted in an independent Confederate States of America, complete with slavery. The series proper starts around World War One, although the series is sometimes known by the title of its prequel book, How Few Remain, which takes place in the 1880s.
The installments of the series :
The Timeline 191 series contains examples of the following tropes: