Here is Timothy Snyder, once Yale professor specializing in the holocaust, explaining how an atrocity like the holocaust could have happened. If you ever asked yourself "how could something so evil have happened" you should definitely watch it: https://www.youtube.com/watch?v=BsKrWLf7Kg4
Likewise it is worth reading They Thought They Were Free. It describes the mental states of denial and inevitability, the rationalization of inaction, and of realizing it's "too late." If you want the quick read you can start at "Each act, each occasion, is worse than the last, but only a little worse." Here is an excerpt: https://press.uchicago.edu/Misc/Chicago/511928.htm
People who have have made it their lives work to study the worst kinds of history have been setting off alarms because they perceive the fires of fascism to be burning here in America right now. Here you can watch such a video (5m) on NYT of world experts on the atrocities of the past warning us: https://www.nytimes.com/video/opinion/100000010157022/yale-c...