Technology

Over the decades since WW2, the popular culture of the allied countries has typically portrayed Nazis as caricatured crazy monsters. They are treated as strange, other, and non-human. This seems to have thoroughly undermined people's ability to recognize Nazism as a destructive force that lurks in people, whether they're German or American or any other nationality. Any society has the potential to fall into this. The unreflective complacency of the WW2 victors after defeating Nazis once has led to a complete lack of awareness that it's an ongoing job to keep your society from falling prey to fascists.

For a while the collective memory of those who lived through the war protected us, but when that generation died off the lessons were forgotten. Some fell into fascism without realizing it because they assumed they were by nature better than Nazis, while others failed to notice the threat until dangerously late.