The victorious opposition - Harry Turtledove

Turtledove's alternate history of America in the last 150 years
continues . . . The final book in the American Empire sequence takes
the violent American civil war (which has become a world war) to the 1930s.

Seventy years have passed since the first War Between the States. The North American continent is locked in a battle of politics, economies and moralities. In a world that has already felt the soul-shattering blow of the Great War, North America in 1934 is the powder keg that could ignite another global conflict.

The Victorious Opposition is a drama of leaders and followers, spies and traitors, lovers and soldiers. From California to Canada, from combat on the high seas to the secret meetings where former slaves plot a desperate strategy for survival, Harry Turtledove has created a human portrait of a world in upheaval.