This is a small gem. I mean, the idea that the centrist parties came very close to muddling through.
Even since my teenage years, I rather believed that the twin blows of first hyperinflation and then the Great Depression made some desperate, radical political shift almost inevitable. And it may not have been.
Indeed it may not have been! I think it could be as simple a matter as "No Hitler;" say he got killed during the Great War. Then it is quite likely that there would be no party corresponding exactly to the OTL Nazis--there would be the original version that Hitler took over, but it would be more radical in the economic sense (probably still racist) and much smaller and weaker, since it would fail to appeal to the "Mittelstand" nor gain upper-class supporters; it would just be a third-rate club of brawlers with some loony theorists hanging around. Most of the people who formed the core of the OTL Nazi party would still be around and have to go somewhere, but the odds are fairly good they wouldn't all coalesce into one party, so they'd be in the fringes of politics one way or another--either big cheeses in small parties, or peripheral members of big ones.
If there is no Nazi Party with the wide basis of support Hitler developed, and led by a ruthless leader like himself ready to horse-trade almost anything to get supreme power, I imagine the Weimar system would have muddled through; rightists would have taken up dictatorial powers to some degree , but not held on to them once the crisis started to pass.
In turn I think that means no European war, not in the 1940s and conceivably not ever up until now--very possibly there would be war in the Balkans, and eventually there would be some confrontation that might well escalate to more or less major wars of liberation in the colonies; someone other than China going to war with Japan seems nearly certain.
But other than that--I see no reason for France, Britain, Germany to ever fight each other, nor any reason for the smaller states of northwest Europe to come to blows; they certainly won't be fighting each other over their colonies--much more likely they will be drawn into a tight alliance of mutual support of their colonial policies, against the colonized. Without a Nazi regime in Germany, I don't believe Mussolini would dare to upset the status quo in Europe by much--again excepting the Balkans, where he might be the cause of much of the instability there.
Stalin, or any alternate Soviet leader, would I think sit tight, perhaps grabbing a little bit of territory here or there as opportunity affords--by which I mean, in cases where the losing nation has also so alienate Western European support that the Soviets can get away with it. But wherever confrontation might lead to an outbreak of general war with Western powers, they will back off; continuing to build a vast and sporadically modernizing army, they won't use it. The United States, and quite possibly Britain and France, seem likely to eventually get drawn into war with Japan; conceivably the Soviets are involved on one side or the other--but they won't entangle themselves with Japan unless either they think they can win or they have a surefire exist strategy. I think USSR allying with Japan on any terms is exceedingly unlikely (though one could sketch out a scenario). More likely, Japan gets into trouble with the Western powers, by alienating the USA and then threatening French and British (and Dutch, and US) colonies, and the Soviets opportunistically pile on as Japanese power collapses.
So it would hardly be a world completely free of war, but WWII as we knew it would be absent, reduced to regional wars in the Balkans and the Sino-Japanese war; meanwhile various revolutionary insurgencies would break out in the European colonies.
But on the whole, a world much less torn by war.
All thanks to Hitler not being in it.