The death eaters are really not subtle, as far as metaphors go. They are all about emphasizing the importance of having "pure blood" (wizarding, that is), and they march around with masks on. Even the most casual scholars of U.S. history can recognize a reference to the Ku Klux Klan, wethinks. (And not for nothing, the Klan actually calls some members wizards.)

And then, of course, there's the Dark Mark. We think Igor Karkaroff says it best when he's talking to Snape:

KARKAROFF: It's a sign, Severus. You know what it means as well as I.

He's talking about the Dark Mark tattoo on his arm flaring up, but the sentiment goes for us as well: we know very well what the Dark Mark is meant to represent. It's a branding that indicates allegiance to Voldemort's ideas about wizardly blood purity. You know, like a swastika.

Again, not super subtle, if we know our history. The Death Eaters and their symbols are definitely callbacks to some of the most horrific examples of racism we've seen in human history.

Let's hope wizards are better at solving those problems than humans have been, right?