This is fourth and last book in the third series in this particular alternative historical timeline, all of which are based on the premise that the Confederate States of America won the American Civil War (referred to as the War of Succession in these books) and still exists.
The series which ends with this volumes covers a time period that corresponds to that around the Second World War in our own history. There are many corollaries between the different time lines and, in his own inimitable style, crafts a story that is internally consistent and highlights the natural development of human society from our own.
Turtledove is a masterful storyteller who has managed to keep my attention on a group of characters and a grand narrative across a total of eleven books, all based on a simple ‘what if’.
I would highly recommend this whole timeline series.