It is something that was present everywhere. People tend to value their own group than the other. Jews tended to keep to themselves, which had two reasons: the

It is something that was present everywhere. People tend to value their own group than the other. Jews tended to keep to themselves, which had two reasons: they were forced to by laws in many countries (e.g. Ashkenazi group evolved to have good math skills mostly because they were forbidden from owning land etc. but were allowed to be merchants) and by Jews themselves tending to one another and keeping outsiders out (which is quite natural for any group, but not to that extent). Consider what happens in most cases when w given ethnicity moves out of their country - they integrate in century or two (see USA). Jews do not, at least orthodox ones (which were majority before I think). Similar thing happens with other immigrants - if they don't integrate, they are feared. If they have different religion even more so. Countries outside of Germany during (and before) WWII didn't have state level killings of those "alien" groups.