Written in 1889, The Great War Syndicate is about a cabal of wealthy businessmen who plan to start a war between European states so they can profit from selling weapons to both sides.
Count this one as a “wars of futures past.”
19th Century
The Great War In England 1897
The Great War In England 1897 is an 1894 novel about an invasion of England by France and Russia. Interestingly, Germany comes in on England’s side.
It’s an interesting entry in what you might call the literature of the wars of futures past.
La Guerre Infernale
La Guerre Infernale is a 30 issue illustrated magazine published in 1908 about a future war between France and Germany.
Even if you don’t read French, the Victorian Science Fiction illustrations are terrific. Lots of inspiration for your VSF games.
The Battle of Dorking
Published in 1871, The Battle of Dorking is a novella about a German invasion of England. Set fifty years after the defeat and dissolution of the Empire, it is framed as the reminisces of a veteran to his grandchildren.
You might call this a novel of a war of futures past.