Robert Harris’ Fatherland was one of the best novels I ever read, and barely scrapes in as science fiction simply because it maps out an alternate history: detente between the US and Nazi Germany in the 1950s.
I decided to read more What If? stories, and found a book (called "What if? from vague memory) containing series of non-fiction suppositions which were interesting if dry.
I then read a very disappointing novel involving the Cuban Missile Crisis, in which General Curtiss Le May launched a strike on Cuba and the USSR, in bare retaliation for which the USSR destroyed Washington Dc and Florida. The story slowly revolved around the idea of an “anschluss” with England. It was fragmented and badly written. I can’t even remember the title.
I’ve since read The Difference Engine by Bruce Sterling and William Gibson which entertaingly postulated the rise of computers in steampunk Victorian England.
Robert Heinlein’s “The Number of the Beast” has British/Russian antipathy from the Great Game continuing on Mars: American independence never evolved and Australia belongs to the French. Regrettably Heinlein never fully played this out: it was a very ancillary scene in the book.
Any others anyone can recommend?