In a recent radio programme for the BBC J.K. Rowling discussed Voldemort's personal ideology and philosophy.
Bridget Christie: When there were studies that found that people who read the books had more empathy and were more tolerant was that something that was quite a...?
J.K. Rowling: Well, it's an amazing thing to read. And those themes are deeply embedded in the books. Ideas of being different. Racism is obviously there in allegorical form. Totalitarianism is there because Voldemort is obviously an authoritarian...I wouldn't say he's a populist but I suppose he's a kind of nationalist. So, yeah, those ideas are all in there and it's an incredible thing to think that people would have softened in their attitudes because of reading them.
(The Museum of Curiosity, Christmas Special, BBC Radio 4, 23rd December 2019).
Plainly there's plenty of evidence that Voldemort was a totalitarian and an authoritarian. The claim that he was a nationalist strikes me as being less clear. Yes, Voldemort restricted his campaign of terror to Britain and didn't show much interest in the rest of the world. But he was much more self-evidently pro-wizards than he was pro-UK.
I can't really think of any examples from the books where Voldemort exhibits nationalist tendencies. Are there any such examples? (I'm primarily interested in the books and Pottermore rather than other forms of canon).