...Like the puddles of human waste that polluted the water of London and created epidemics of Cholera.

Sure, Cholera existed before the shit was running in the streets, but the filth provided a reservoir from which it could emerge and take firm hold of the populace.

Fascists and authoritarians have always existed. Yes Putin and his oligarchs seek to erode and subvert democracies... and yes, that is exactly why they worked to build up Trump- and why they boosted brexit and the far-right all across europe. By turning the liberal democracies into authoritarian oligarchies Russia can say to their people "look, the alternatives to our kleptocracy are all just as bad or worse than what you have here..."

But the efforts of Putin and Trump would amount to little if there wasn't the puddles of human filth willing to provide a growth medium for the disease.
Were there not small minded bigots yearning for a cruel daddy, these fascists would amount to nothing.

Had people said to Hitler 'shut the hell up and get back to painting, you bigoted little freak!' then millions would have lived... sadly there was no shortage of filth willing to take up his words, amplify them, and eventually act on them.

As you said, this is a recurring social phenomenon. The reason for this can again be viewed in terms of epidemiology. When a fascist plague burns through a populace and is finally driven into remission, there is a natural resistance to the disease left in the survivors. They are inoculated by history, but this resistance fades over time. As the tired old phrase says- 'Those that do not learn from history are doomed to repeat it'. This is exactly why fascists erase and rewrite history- it is the cure to their disease.

So we can argue over what is responsible- "is it the disease or is it the filth that allows it to flourish?" ... no amount of philosophizing will change the fact that both need dealt with aggressively if we are to survive the plague.

We have human shit running in our streets, we need to decide that we will not tolerate it.