What should had happened if Nazist Germany had won World War II? This novel is a possible answer to the question and it's a rare example of "earthly science fiction".
Quoting the Italian title of the book, Swastika is over the sun and Dick tries to explain us the reasons why.
Yet I remember how I was disappointed while reading at this book for the relatively few interesting elements given by the author. I mean, starting from such a premise Dick could use more imagination while he hadn't, mantaining a low and dry profile in narration.
On a similar theme I'm curious to have a look to the more recent "The plot against America" by Philip Roth which imagines the anti-semite aviator Charles Lindbergh defeating Franklin Delano Roosevelt on the American 1940 presidential elections.