Okay, there's a distinction here that should be made. The industrial evolution in the 19th century led to the rapid development of technology which strongly impacted and swiftly changed many elements of life in the industrializing world; this was very obvious in applications like transportation--the appearance of steam-ships, railroads, automobiles, and experiments in flight--as well as the beginnings of industrial application of electricity for lights, telegraphs, radio, telephones, etc. A substantial part of early science fiction dealt with either hypothetical inventions and technology, like Jules Verne's Journey to the Center of the Earth (1864) and Twenty Thousand Leagues Under the Sea (1870), or with "gadgetry," in the sense of Hugo Gernsback's Ralph 124C 41+ (1911).

None of this fiction was "steampunk" at the time, because the word itself wasn't coined yet. The "punk," rebellious, do-it-yourself attitude was applied to New Wave-style science fiction literature in the early 1980s as cyberpunk, among whose major stars were William Gibson, Bruce Sterling, Pat Cadigan, John Shirley, Bruce Bethke (who actually coined the term), etc. While "cyberpunk" fiction carried with it a lot of the tropes of existing science fiction, the new generation of writers brought with a new attitude. As Sterling would write in Cyberpunk in the Nineties:

Anything that can be done to a rat can be done to a human being. And we can do most anything to rats. This is a hard thing to think about, but it's the truth. It won't go away because we cover our eyes.

The later hallmarks of cyberpunk, based on works like William Gibson's Neuromancer (1984) because cybernetic enhancement of the human body, human alienation through technology, a worldwide computer network, a near-future corporate dystopia, etc. - the kind of setting popularized by works like the movies Bladerunner (1982) and Alien (1979) - lived-in futures that were far more visceral than the gleaming rocket ships imagined during the Golden Age of Science Fiction.

In 1990, Gibson and Sterling collaborated on a novel titled The Difference Engine. This was essentially a cyberpunk novel set in an alternate, Victorian past instead of a near-future - but the aesthetic was the same; the difference engine itself was a primitive computer, this novel simply imagined a Victorian setting where the technology was embraced more whole-heartedly and pursued more rigorously than happened in reality. It's basically the prototypical steampunk book, both for the idea and the attitude.

But it didn't stay there, and arguably it didn't start there; people cast back looking for and found precursors in 19th and 20th-century fiction; Gibson & Sterling weren't the first to use a quasi-Victorian setting for their speculative fiction, or the first to extrapolate from 19th century tech into bold new directions. The actual name was coined by writer K. W. Jeter, riffing off "cyberpunks" in 1987:

Personally, I think Victorian fantasies are going to be the next big thing, as long as we can come up with a fitting collective term for Powers, Blaylock and myself. Something based on the appropriate technology of that era; like ‘steampunks,’ perhaps….

I don't have time right now to give this question the answer it deserves, but I want to mention three specific books I've read over the past couple of years, which I think speak to this question:

• Steaming into a Victorian Future: A Steampunk Anthology edited by Taddeo and Miller. This is a collection of academic essays looks at the contemporary (post 1980) steampunk aesthetic, in terms of not only how it emerged out of literary and cultural discourse about the role of technology in shaping human culture in the 1980s, but also at how people use steampunk as an ideological lens to interrogate questions about cultural patrimony, and more broadly, inspects how acts of re-imagining the past is not just a form of escapism, but a way of asking questions about the norms and circumstances of the present. The essay "Enacting the Never-Was" (by Barber and Hale) is the chapter that addresses these themes most directly.

• Clockwork Futures: The Science of Steampunk and the Reinvention of the Modern World by Brandy Schillace. This book uses the steampunk movement as a jumping-off point to examine how the role of engineers and scientists in fiction and popular culture over the past 200 years has shifted in response to popular conceptions, misconceptions, and anxieties about the role of technological and social changes. Schillace does a particularly good job of showing how even the seemingly-triumphalist technology heroes of the early 20th century pulps still showed a sense of ambiguity towards the idea that "progress" was an unalloyed good, and she also looks at how some very plausible scientific ideas, like fluidic computing, are not widely seen in "steampunk"-style fiction because they don't fit into the ideological lenses what we use to understand the development of technology over time, and what reveals about popular ideas around the history of technology.

• Steampunk Prime, edited by Mike Ashely. This is a collection of fiction, but it consists entirely of works of speculative fiction originally published between 1880 and 1914. Many of these stories are not easily available and supposedly were originally published in periodicals which exist now only in a handful of British archives. These stories are a direct look at how the late Victorian writers themselves imagined the future, or at least the progression of their own social and technological trends. One interesting thing you notice is the general absence of "steam", but rather that electricity is the magical force that will make all wonders possible. There's also quite a bit very prescient wondering about the role of instant communications breaking down social bonds, and even a surprising about of speculation about the possibilities of genetic engineering and AI. Plus ca change.. /u/AncientHistory, if you have read this book I should like to hear your thoughts on it.