[Astromancer]

Try this idea, place a millitary genius in the family of a key supporter of Louis Napoleon (in our world the kid dies in infancy). The French still start the Franco-Prussian war outnumbered and outguned, but with a general of genius. Bismark finds the Prussian army fought to a standstill. Deals are made. France keeps Alsance and Lorraine and no reprerations are paid. Louis stays on the throne, the Prince Imperial stays in Paris and becomes Napoleon the IV. France is reactionary but has strong generals for the next century.

Germany and France stalemate each other and the British Empire survives into the 21st century as the dominant power on the planet. The USA becomes the home of democratic socialism and progressive thought .