"Alternate History: The How-to of What Might Have Been" is a non-fiction essay by Harry Turtledove, first published in Writers Workshop of Science Fiction and Fantasy (2013, Michael Knost, editor) and reprinted in We Install and Other Stories (Open Road, 2015). Turtledove attributes the origin of alternate history to being a "playground of historians and politicians on a lark" before it was co-opted by science fiction writers such as L. Sprague de Camp and Poul Anderson, which caused it to become primarily a subgenre of SF. He argues that AH writers are influenced by the world they live in; for example most AH writers in the generations immediately after the death of Napoleon I wrote Napoleonic speculations, whereas the AH market in Turtledove's own lifetime, coming following World War II, is saturated with alternate histories of that particular war, drowning out World War I scenarios. He explains the "how to" as taking a break-point both historically significant and interesting to read about, creating a situation where it could have plausibly gone the other way, being well informed on the period being dealt with, and remembering that if one thing changes, other things will too, until everything has changed. He warns not to make internal mistakes that a large number of people will inevitably spot, such as attributing omnipotent fuel capacity to Royal Air Force fighter planes of the 1940s, or an unrealistic price to a pair of shoes in 1902 - AH is a research intensive subgenre. Along the way, Turtledove uses examples from his own writing to illustrate his points about the most common AH mechanisms, citing specific examples from Gunpowder Empire, How Few Remain, In High Places, A World of Difference, "Down in the Bottomlands," A Different Flesh, and The Two Georges, with subtler allusions to The Guns of the South and the Days of Infamy series.
Along the way, Turtledove offers a humorous, playful bit of revealing advice alluding to his own willingness to break his own rules for the sake of a gag, citing an example from The Two Georges: "This is one of those places where you can cheat. If you've got a world where the American Revolution never happened, Richard Nixon won't get born (one possible advantage to learning different words to "America the Beautiful"). But if you need a used-car salesman called Tricky Dick in the late twentieth century of that world, go ahead and stick him in. Just be aware that you are cheating, and then sin proudly. Don't drop him in for no better reason than that you haven't thought through the consequences of your change."