Americans - even Americans like Bernie - have an incredibly shallow understanding of history. They will recall a few key words and ideas from their history classes, but probably even more just from the environment around us, which is skewed towards reproducing capitalism. So they understand historical subjects only at the most basic level and usually not in a way that is correct.
I don’t think historical ignorance is a huge problem in itself. The bigger problem is, despite their incredible levels of ignorance, Americans will insist their understanding of history is inviolably correct; No American will ever say “well, you sure seem to know a lot about Stalin, I don’t know anything so tell me more”. Suggest anything about Stalin outside of “authoritarian dictator who kiled millions and made everyone clap” and Americans will INSiST you are wrong and they are right, regardless of who has actually put in any work.