This is an alternative history novel with novel twist to it. It addresses an important issue of social and geopolitical importance, which is not what happens in most counterfactual history books.
The most widely read counterfactual histories wander off into an unrecognizable future which no thinking person can believe, given the contingent nature of historical events.
The more common variety stop short to give a new ending to a historical event, without exploring the extended ramifications.
Think Turtledove's series of book on an alternative outcome to the American Civil War for an example of the first option, where the whole history of the world is explored though the end of World War II with a divided United States taking different sides in both World War I and World War II.
But as I said, S-Day is different. It starts by imagining that Nazi Germany had avoided war with the Soviet Union in 1941 The reason is not given, is not important, and is within the range of possibility. Simply imagine some new arrangement between Hitler and Stalin that keeps the Nazi-peace in Europe
