In the late 70's to the mid 80's, a number of authors wrote fictional accounts of what they thought World War III would look like (Sir John Hackett's "The Third World War", Tom Clancy's "Red Storm Rising", and Harold Coyle's "Team Yankee" are few examples of the type of writing I'm referring to). Did anyone write similar fiction about World War II prior to 1939? Or is the genre a unique product of a long, tense cold war?
The one that jumps to mine is The Shape of Things to Come by HG Wells. Published in 1933, it was intended to be 'future history', IE: A historical story from a futuristic universe. The set-up in that book was fairly similar, predicting a second World War that would begin in Europe due to a conflict between Poles and Germans in early 1940. He even placed the conflict as starting in Danzig, which was indeed one of the first battles.
That said, the rest of the story was pretty different. France and the Soviet Union aren't really involved, countries remain neutral that were heavily involved, Spain plays a completely different role, etc. Some details were of course correct (the heavy focus of bombing other cities), but instead the war he pictured was more or less a land war, bogged down by trenches like the first war.
The fact that his fictional World War ends in total collapse as everything runs on so long that most governments simply collapse in on themselves was probably the most significant difference, considering it leads to a strange dystopian world that eventually gives way to a utopian world.
It's probably the most notable example I can think (mostly due to HG Well's prominence), but there's definitely other examples.
They certainly did. The "Future War" genre (see the Encyclopaedia of Science Fiction entry for a good summary) goes back at least to the 18th century, but the most direct descendent of the "drama-documentary" of Hackett & co. is probably Chesney's The Battle of Dorking from 1871 depicting a successful German invasion of Britain. It was popular enough to spawn a whole "invasion" genre over the next 40-odd years featuring actual, or threatened (e.g. The Thirty-Nine Steps), invasions, even spoofs such as P. G. Wodehouse's The Swoop! or, How Clarence Saved England: A Tale of the Great Invasion ("England was not merely beneath the heel of the invader. It was beneath the heels of nine invaders. There was barely standing-room.")
The advent of the airship and aeroplane brought a new threat as envisaged by e.g. H. G. Wells in The War in the Air of 1908 and The World Set Free of 1913 (featuring atomic bombs), the actual use of air power in the First World War including city bombing meant aircraft played a large role in inter-war Future War fiction. As aeroplanes had progressed from barely carrying their crew at the start of the war to a ton of bombs and more at the end of it there was an apocalyptic strand to some of the writing, envisaging the impact of ever larger fleets of faster, heavier bombers unleashing explosive, incendiary and poison gas bombs on cities. The worry of a "knock-out blow", a massive, devastating attack that would leave a country unable to function, featured in both serious military and political writing and fiction - as Brett Holman notes in The Next War in the Air "indeed, there was little difference in content and, to an extent, style between knock-out blow scenarios in fiction and non-fiction". Examples include the Earl of Halsbury's 1944 (written in 1926), E. F. Spanner's The Broken Trident also of 1926, McIlraith and Connolly's 1934 Invasion from the Air, and Leslie Pollard's 1935 Menace. The military theorist Giulio Douhet followed his Command of the Air of 1921, one of they key works on air power, with an illustrative novel, The War of 19--, in 1930 envisaging a war between Germany and France and Belgium that effectively lasts a single day as German bombers obliterate Franco-Belgian air forces and cities.
Wells continued his works; The Shape of Things to Come of 1933 envisaged a war between Germany and Poland in 1940 with heavy city bombing, but rather than bombing being a knock-out blow his war bogged down and dragged on, much of the book concerned with the post-war 20th century. Of course The War of the Worlds had expanded the invasion genre into more speculative science-fiction with Martians and their heat rays, but "death rays" also figured in more grounded inter-war fiction as authors extrapolated on the possibilities of X-Rays and the like, either to actually kill, or to remotely detonate explosives, or to stop engines; the Air Ministry initially asked Robert Watson-Watt to investigate the possibilities of a "death ray", on proving such to be impossible he persuaded them instead to focus on the possibilities of radio detection leading to Britain's radar network of the Second World War.
Further reading:
I F Clarke, Voices Prophesying War: Future Wars, 1763-3749
Martin Caedel, "Popular fiction and the next war, 1918-1939", Class, Culture and Social Change: A New View of the 1930s
Paul Williams, "Race, War and Apocalypse before 1945", Race, Ethnicity and Nuclear War: Representations of Nuclear Weapons and Post-Apocalyptic Worlds
Paul K. Saint-Amour, "Air War Prophecy and Interwar Modernism", Comparative Literature Studies, Vol. 42, No. 2
William J. Fanning, Jr., "The Historical Death Ray and Science Fiction in the 1920s and 1930s", Science Fiction Studies, Vol. 37, No. 2
Amusingly, an example is the 1938 edition of the Nostradamus Prophecies by H. de Fontbrune (which I happen to have at home)^1. It is a fun read, as while he predicted that a second world war would happen and that it would be caused by Germany (which was not that hard at that time), he described a scenario where France and Italy were invaded through Switzerland and other fantasy history. Looking online, this edition seems to be found on various online book retailers.
^1 : This is H. de Fontbrune Sr, not his son who also wrote Nostradamus interpretations in the 70s and 80s (also a fun read).