Anomaly UK has a theory about Weimar Germany and how democracies end:
The popular theory, which I’ve alluded to previously, is that the big event was this chap Hitler. He was some supernatural weirdo from Hell, who, like a false prophet, inspired the normal, liberal people of Germany to give up their democratic birthright and follow his dreams of securing lebensraum for the master race, etc, etc.
Then there’s that slightly odd bit where he didn’t actually win the election, but he did fairly well and it sort of counted as near enough, so he was declared Chancellor and allowed to take over everything in sight. It kind of seems like some sort of dodgy conspiracy, but it’s not obvious whose.
My theory, grounded on the above, is that by — what are we talking, 1933? — democracy had so completely, utterly, failed that nobody, least of all those actually running it, could stomach it carrying on one year longer. The only question was what to do instead? There were communists kicking around, but that wasn’t an attractive idea for the ruling class. And there was this Hitler dude, and while he had a bunch of somewhat fruitcake ideas, he seemed to have support, he was serious about changing things, and at least he wasn’t a commie. What else was there? Even the leading democratic politicians didn’t have any better idea than letting him have a go.