Aristopia: A Romance-History of the New World (1895) by Castello Holford is considered the first novel-length example of Alternate History written in English and is among the earliest contemporary Alternate Histories in general. The book is apparently impossible to find nowadays, as it was published by the Arena Publishing Co., which only existed from 1890 to 1896.
Aristopia is interesting in that it takes the general utopian/dystopian literary groundswell of the late 1800s and turns it backwards in time. Holford's puts the founding of a utopian society in the distant past, instead of the far future or some far-off place as was the most common setting in literature.
In Aristopia, settler Ralph Morton discovers a reef made of solid gold off the coast of Virginia. Morton uses his newfound wealth to craft a society based on the theories in Thomas More's Utopia, with some innovations of his own included in the bargain. In the country Aristopia (which incidentally is Greek for "the best place"), all land is owned by the state and is merely leased to private individuals and businesses. Large-scale trade is controlled by the state, and there's limited inherited wealth.
Morton and his government eagerly accept industrious immigrants such as Huguenots, Irish fugitives from Cromwell's wars, and northern Italian and Swiss artisans to join their society. The Aristopians purchase more land from the Native Americans, and expand westward. Morton eventually dies at 100 years old, and his descendants continue his policies. The Aristopians support the American Revolution, and eventually conquer Canada under their own volition. Eventually, Aristopia dominates all of North America except for Mexico.
This and other Alternate History stories -- among them H.G. Wells's Men Like Gods (1932) and Robert Heinlein's Elsewhen (1940) -- explore the possibilities of what the world would look like if things happened otherwise. To Steampunk, Holford's Aristopia and novels of that ilk showcase the imagination and the devotion to logic that writing Alternate History requires.
Holford's story adds a singular, unusual event to American history and details what might have happened if it did occur. Though Wells, Heinlein, and others wrote cross-time stories (where the hero travels to another dimension a la the TV show Sliders where the world is different but the hero is the same), they still present logical points of divergence with our own world. That Ralph Morton discovered a reef of solid gold is paramount to the events of Aristopia. Take that away, and history stays the course it took. And what fun is that?*
*Yes I know it's quite a bit of fun re: historical fiction, but work with me here.
Thursday: Detective Fiction and A Devotion to Logic