By the way, I should clarify that my total disagreement with your thesis on WW2 being single-handedly caused by A. Hitler does in no way imply disagreement with your more general thesis. In general I do believe the “until comes steam-engine-time” theory—that many macro-scale circumstances must be present to create a favorable environment for some revolutionary change; to a lesser degree, I also do think that mostly, when the macro-environment is ripe, one of the many sparks and matches (that are going off all the time, but normally fizz out because the environment is NOT ripe) will tend to start the blaze. But there’s nothing “inevitable” here: these are probabilistic, Bayesian beliefs, not “blind faith” on my part. One can look at all available detail and information about each historical situation and come to opine that this or that one follows or deviates from the theory. I just happen to think that WW2 is a particularly blatant example where the theory was followed (as Keynes could already dimly see it coming in ’19, and he was NOT the only writer of the time to think that way...!); another equally blatant example is Roman history in the late Republic and early Empire—yes, many exceptional individuals shaped the details of the events as they unfolded, but the nearly-relentless march of the colossus away from a mostly-oligarchic Republic and “inevitably” towards a progressively stronger Principate looms much larger than any of these individuals, even fabled ones like Caesar and Octavian.
But for example I’m inclined to think of more important roles for individuals in other historically famous cases—such as Alexander, or Napoleon. The general circumstances at the time of their accessions to power were no doubt a necessary condition for their military successes, but it’s far from clear to me that they were anywhere close to sufficient: e.g., without a Bonaparte, it does seem quite possible to me that the French Revolution might have played itself out, for example, into a mostly-oligarchic Republic (with occasional democratic and demagogic streaks, just like Rome’s), without foreign expansionism (or, not much), without anywhere like the 20 years of continuous wars that in fact took place, and eventually settling into a “stable” state (or, as stable as anything ever is in European history;-). And I do quite fancy well-written, well-researched “alternate history” fiction, such as Turtledove’s, so I’d love to read a novel about what happens in 1812 to the fledgling USA if the British are free to entirely concentrate on that war, not distracted by Napoleon’s last hurrahs in their backyard, because Napoleon was never around...;-) [To revisit “what if Hitler had never been born”, btw, if you also like alternate history fiction, Stephen Fry’s “Making History” can be recommended;-)]
After Napoleon, France was brought back to the closest status to pre-Revolutionary that the Powers could achieve—and (“inevitably” one might say;-) 15 years later the Ancien Regime crumbled again; however, that time it gave birth somewhat peacefully to a bourgeois-dominated constitutional monarchy (with no aggressive foreign adventures, except towards hopefully-lucrative colonies). Just like the fact that following Keynes’ 1919 advice in 1947 did produce lasting peace offers some support to Keynes’ original contention, so the fact that no other “strong-man” emerged to grab the reins in 1830 offers some support to the theory that there way nothing “inevitable” about a military strong man taking power in 1799 -- that, had a military and political genius not been around and greedy for power in ’99, France might well have evolved along different and more peaceful lines as it later did in ’30. Of course, one can argue endlessly about counterfactuals… but should have better support before trying to paint a disagreement with oneself as “absurd”!-)
BTW, in terms of human death and suffering (although definitely not in terms of “sheer evil” in modern ethical conception), the 16 years of Napoleon’s power were (in proportion to the population at the time) quite comparable to, or higher than, Hitler’s 12; so, switching from Hitler to Napoleon as your example would not necessarily weaken it in this sense.
“In sober historical fact”, clear minds could already see in 1919 that the absurdity of the Treaty of Versailles (with its total ignorance of economic realities, and entirely fueled by hate and revenge) was preparing the next war—each person (in both nominally winning and nominally defeated countries) being put in such unendurable situations that “he listens to whatever instruction of hope, illusion or revenge is carried to him on the air”.
This was J.M. Keynes writing in 1919, when A. Hitler was working as a police spy for the Rechswehr, infiltrating a tiny party then named DAP (and only later renamed to NDA); Keynes’ dire warnings had nothing specifically to do with this “irrelevant” individual, which he had no doubt never even heard about—there were plenty of other matches ready to set fire to a tinderbox world, after all; for examle, at that time, Benito Mussolini was a much more prominent figure, a well known and controversial journalist, and had just founded the “Fasci Nazionali di Combattimento”.
So your claim, that believing the European errors in 1919 made another great war extremely likely, “is an unreasonable belief”, is absurd. You weaken your interesting general argument by trying to support it with such tripe; “inevitable” is always an overbid, but to opine that the situation in 1919 made another great war all too likely within a generation, quite independently of what individuals would be leading the various countries involved, is perfectly reasonable.
Keynes’s strong and lucid prose could not make a difference in 1919 (even though his book was a best-seller and may have influenced British and American policies, France was too dead-set in its hate and thirst for revenge) -- but over a quarter of a century later, his ideas prevailed: after a brief attempt to de-industrialize Germany and push it back to a pastoral state (which he had already argued against in ’19), ironically shortly after Keynes’ death, the Marshall Plan was passed (in rough outline, what Keynes was advocating in ’19...) -- and we didn’t get yet another great european war after that.
Without Hitler, but with Versailles and without any decent reconstruction plan after the Great War, another such great war WAS extremely likely—it could have differed in uncountable details and even in strategic outline, from the events as they actually unfolded, just like the way a forest fire in dry and thick woods can unfold in many ways that differ in detail… but what exact match or spark lights the fire is in a sense a detail—the dry and flame-prone nature of the woods makes a conflagration far too likely to avoid it by removing one specific match, or spark: there will be other sparks or matches to play a similar role.