This may be a good place to ask but why the hell white supremacists hate Jews so much? I'd never understood that, is there a particular reason?
Antisemitism has been around for millennia, mostly related to other religions. More secular Antisemitism stems from a couple different sources.
First of all, since Jews have historically been an exclusive people, they were always viewed as "others" and never an organic part of a given nation. If there were German Jews, they weren't Germans - they were Jews in Germany, as far as the Christians/whites were concerned. For nationalists and racial theorists, this obviously set them apart as suspicious. Why trust a group of "rootless cosmopolitans" who didn't share your culture and blood? Ironically, Jews often did try to integrate while maintaining their own culture, but the hostility towards them ensured their own distinctiveness.
Secondly, by being separate, there were certain things Jews were not allowed to do but certain other things they COULD do. For example, Christians were prohibited from usury, but Jews were not. This allowed some Jews to get involved in finance, leading to the stereotype of the "greedy Jew". This is also why European monarchs had "court Jews" to provide them funding. This led to conspiracy theories about secret globalist Jewish cabals, who want to control the world and rid it of their archnemesis, the whites, by breaking down their cultures through multiculturalism. This is why you see white supremacists constantly ranting about Jews being behind interracial marriage and immigration. They think that the successful Jews in the media and industry, who are proportionally overrepresented (since, you know, they strive to achieve to protect themselves), are trying to use their resources to destroy the (White) West.
For the Nazis it was sort of like that, since they believed the Jews were behind both capitalism and communism in a scheme to destroy European culture, since both are global in nature rather than national, and both put economics at the center of life instead of traditional culture. Hence the Nazis tried to genocide them all to "save" Europe.
Ironically Jews tend to score high on the pseudoscientific IQ tests that white supremacists bandy about, so racists claim that this is because Jews are naturally crafty.