What you are describing sounds like it would fit in the genre of Alternative History. Note: Americans often call it "alternate history" because they can't speak English properly :-)
Alternate history or alternative history (British English), sometimes abbreviated as AH, is a genre of fiction consisting of stories in which one or more historical events occur differently. These stories usually contain "what if" scenarios at crucial points in history and present outcomes other than those in the historical record. The stories are conjectural, but are sometimes based on fact. Alternate history can be seen as a subgenre of literary fiction, science fiction, or historical fiction; alternate history works may use tropes from any or all of these genres. Another term occasionally used for the genre is "allohistory" (literally "other history").
This is way off-topic here, because there are no correct answers, only speculation.
WorldBuilding Stack Exchange allows speculative questions on AH.
Science Fiction and Fantasy Stack Exchange allows discussion of the genre.
There was already a proposal to create a Stack Exchange dedicated to it. It failed.
I, for one, wouldn't support it, because I think it better suits the speculative discussion in the pub format than the "seeking the one best answer" of Stack Exchange.