Similar conditions provoke similar results. Not identical, but similar enough that the basic pattern and structure is recognizable. You don't need death camps and an invasion of Poland to have fascism...

A period of economic growth and political progress produce a thriving and prosperous middle class with what it perceives as a bright future.

But conditions change, either because of corruption, stagnation, or perhaps just plain evolution and history, and suddenly that middle class senses a sliding back into its grim working class misery and oppression. My parents' generation were old enough to remember what it was like growing up during the Depression. They could still remember hard times and they passed that knowledge and fear onto their children, who lived long enough to see the brane new economy start to sputter and fail. They become desperate, frightened, desperately seeking scapegoats to blame their anticipated bad future (real or imagined) on. An unscrupulous elite seizes on this anxiety to create chaos, to set one class or race against another for the benefit of their own agenda. Divide and conquer, its the oldest strategy in history.

The end of the Great War and the start of the Great Depression set the stage the last time, the end of American Hegemony and the crumbling away of the New Deal in the last quarter of the 20th century set the conditions again for a repeat. We even have our own version of the Spanish Flu to complete the symmetry. And the ghost of Communism has been resurrected from its Cold War grave to play its usual role.

'Fascism is the dictatorship of the middle class.' Its not just ole ER's catchy slogan, its an observation based on the perception that similar conditions lead to parallel results. No, there is no magic theme that runs cyclically through history. Its just similar events leading to similar responses. Its not magic at all, or coincidence. Water just flows downhill.

I think Mel Brooks understood it very well.