I have a serious problem with the description in that "ERBzine" about international communications & travel in 1899...
We can assume that the world was not so tightly woven together in those days. Thus, for America and for Europe, England was a remote far off country. In 2001, the entire world watched the World Trade Centres fall. But 1899 is a different country, communication is slower and less immediate. The telegraph could splash the news of the Martian invasion of England onto front pages in America, but the information will come through laboriously slow as a series of dots and dashes, there will be no photographs, descriptions and reports will be terse and second hand. There won’t be front page photos, live television, or endless camcorder records. At best, you’ll get a few badly drawn sketches based on secondhand information.
In short, for much of the world, the impact of a Martian invasion of England, might not have the same immediate and worldwide impact as a major terrorist attack or disaster like the Tsunami in the modern day.
The world of 1899 was far more accepting of the notion of life, of intelligent life, on other worlds, so that would not necessarily have been as shocking. Meanwhile, a number of factors would have limited the shock and acted to restore complacency. The invasion seemed confined to England, and the invasion was remarkably short lived, only a matter of weeks. Finally, the Martians simply were unable to cope with Earth’s conditions, clearly shutting the door on the whole matter.
So, one might imagine a stir for a year or two, but eventually, people would settle down, get on with their lives and forget about it. Particularly when no further invasions are forthcoming. I imagine the English would still be somewhat traumatized, but John Carter, Gulliver Jones and Ulysses Paxton are all Americans.
That is rather contrary to what I have read about and from those times - there was a rather large amount of communication across the Atlantic, as well as travel - and the doings of the upper class in Paris & London were of immense interest to the upper classes in the US.
There would be lots of photographs crossing the Atlantic on all the ocean liners, mail ships, and so on - as well as newspapers and people.
So Americans would be well-informed about the Martian invasion, which does mean that the American people would be shaken and disturbed profoundly by the events in England.
Probably isolationism takes hold much earlier than historic, with proponents of American expansion overseas like Teddy Roosevelt finding themselves shunned and ignored. It is likely this that forestalls the Spanish-American War of 1898 - which helps lead to all the divergences mentioned later in the article.
Finally, and this is obviously conjecture on my part, the War of the Worlds may well have had an impact on Burroughs Earth. In the Moon Maid, Burroughs writes that the first world war continued, almost uninterrupted, off and on until the 1960s on Earth. In our world, of course, there was an almost 20 year gap between the two world wars, to be followed by a cold war through the '60s. In Burroughs world, the war seems to have been an almost continuous, generations spanning conflict, with perhaps shorter periods of peace and stability.
Well, Burroughs himself set a novel in that "prolonged World War" setting - Beyond Thirty
, which is a short science fiction novel by Edgar Rice Burroughs. https://en.wikipedia.org/wiki/Beyond_Thirty
It was written in 1915 and first published in All Around Magazine in February 1916, in which we find:
The story was heavily influenced by the events of World War I, and reflects U.S. sentiments at the time of writing. When the war broke out, Americans were predominantly isolationist and wary of being drawn into a European war. Burroughs imagines a future two centuries onward in which that view prevailed and the western hemisphere severed contact with the rest of the world. Consequently, the eastern hemisphere has exhausted itself in war and Europe has descended into barbarism while the Americas, sheltered from the destruction, have continued to advance and joined peacefully into the union of Pan-America. By the twenty-second century the entire world east of the 30th meridian west and west of the 175th meridian west has become terra incognita to Pan-America.
In 2137, Pan-American Navy Lieutenant Jefferson Turck is commander of the aero-submarine Coldwater, tasked with patrolling the 30th meridian from Iceland to the Azores.
After many adventures,
Communications between the hemispheres are re-opened, with commerce to follow, and Turck, despite violating the edict against crossing the 30th meridian, is hailed as a hero in Pan-America.
So we see that the world of John Carter, Barsoom, and H. G. Wells' Martians is indeed a parallel world, and not a secret part of our own history. In other words - any Barsoomian adventuring after the arrival of John Carter can see whatever changes on Earth you want to create.