The series is based on the 1962 novel of the same name by American science fiction author Philip K. Dick. The story is an alternate history of the world in which the Axis powers won World War II. The United States has been partitioned into three parts: The Japanese puppet state of the Pacific States of America, which comprises the former United States west of the Rocky Mountains; a Nazi puppet state that comprises the eastern half of the former United States; and a neutral zone that acts as a buffer between the two areas, called the Rocky Mountain States.