The bigger issue would be if the fascists and authoritarians we did have like Mussolini, Metaxas, Antonescu etc had actually started attacking other nations (okay,
important nations, sorry Albania). That could have easily dominoed into, if not a Second Great War, certainly a stampede of smaller ones.
As is, we got lucky - as Richter says - that Italy and Greece went to blows. Italian fascism was discredited, the Hellenic forces were weakened enough for Turkey to try it on, and the resultant war between them led to the Royal Navy and RAF "discouraging" the Turks. The system of goverment was discredited. (And that still got almost two million people killed, half of them Greeks, and meant the Asian War had a chance to start, so thank Christ we didn't get anything bigger)
for another, the Maginot line could have stopped any German attack.
There's a bunch of takes - Turtledove did one in "The Man With The Iron Heart" - where the Fascists go through Belgium again. That relies on Britain being either weak or unwillingly to get involved due to concerns over Japan though. And to do
that, Turtledove had to have George Lansbury running Labour in the 30s rather than Uncle Arthur and then Clynes.
having the French and British be foolishly enabling of that regime to say balance out the USSR's influence on Eastern Europe
Ah, you've read the Turtledove?
To be fair, he had Stalin running the USSR at the time and that would've certainly been a threat, a plausible one too. Stretching a bit to say a clearly expansionist fascistic government would be the weapon of choice for restraining Stalin though, you don't
literally fight fire with fire.
There is a really nice Kim Newman one on fascist Germany though. Joh Fredersen of Metropolis - so it's not a hard AU, sue me - brings horror and blood to Europe to see his grand dream come true but just a generation after, nobody in the 'free world' cares as long as the Deutchtropolis continues to sell us shiny things. Take the sci-fi and meta out, that still feels like a thing that would happen.