Friend of the Retreat Jon Mollison published a post today on the origins of Science Fiction, predating E.R. Burroughs by over a decade: Robert William Cole. He wrote a story titled "The Struggle for Empire: A Story of the Year 2236", published in 1900 (so 12 years before E.R. Burroughs' A Princess of Mars), which is in the Public Domain and so can be found here at Google Books.
As Mollison's post shows, this tale is a true and proper Scientific Romance--what Science Fiction, true and proper, actually is--and therefore I put to you that this story was an influence on Edgar Rice Burroughs. Not the influence, of course, anymore than Kurosawa was this influence on George Lucas for the original Star Wars film, but an influence- as a proof of concept. Quoting the post's summary of what goes down when the Big Conflict kicks off, it's not hard to see what E.E. Smith had as a baseline to top.
- Fleets of thousands of space ships flung headlong into days’ long battles
- A rain of debris over the continents, mountains, cities, and seas of Neptune
- In keeping with John C. Wright’s definition of “space opera” the blowing up of not one, but two moons, at the same time
- Three-dimensional naval tactics, and
- The frantic last minute search for a savior weapon that might knock the bombarding Sirian ships out of the tropical skies above London.
The other thing this shows is that John Campbell's push, putting the genre into a ghetto and making it all about Big Men With Screwdrivers (i.e. Porn For Werner Von Braun Type), really is a heresy. When you strip the Romance out of the genre, you're engaging in cultural iconoclasm. It is not a surprise to me anymore that that rejecting Romanticism led to genre ghettoization because by stripping out the wonder you also strip out the beauty and the ties to (believe it or not) tradition that makes any body of literature able to hold the substance that carries meaning to the audience. It's exactly the same thing that you see to college girls who go Feminist and deliberately make themselves ugly and wretched in service to that Satanic ideology.
Add this to the To Read pile, and revise your historical timelines accordingly.