Alternate history, by its very nature, is one of the most easily-ploughable fields in genre fiction because literally all one must do is change a single historical event and then logically extrapolate the repercussions. Harry Turtledove has made a career out of doing this.
Sometimes, though, alternate history doesn’t require telling the reader what the crisis point was that got changed. Sometimes, the reader just needs to know things are different. And that’s where The Mirage by Matt Ruff begins.