Jews were always sequestered away from society in Europe, either by their own accord or because the natives thought them to be damaging to the culture. The truth is that Jews (as in Jewish organizations and many Zionists or Marxist leaning Jews) never accept a culture or people other than their own, and because of this, Jews hold their people above any other ethnicity.

The Jewish Talmud treats non Jews as subordinates. Many passages even openly say that mistreatment of Gentiles should go unpunished, and that if the Gentiles knew what the Jews thought of them they would kill Jews openly. There is a specific reason why religions like Islam and many nations take a hard line against Jews; it's because Jews are taught that all others are below them, and deserve to be lied to and cheated.

Now this does not apply to all people of Jewish decent or a faith; as they typically know nothing of their religious doctrine or refuse these teachings. The historic understanding of the Jewish faith and people is no longer prevalent, but it is relevant to the Extremists that do use it. It's the Zionists, Marxists, and Israeli-interest minded that deceive the west, not the 'oh my grandfather was a Jew in 1920's Poland so that makes me Jewish too' Jew that are much more common. Jews are only a problem when they seek power over whites and use them as a means to supporting their interests, not just because they are Jewish. If this happened with any other group trying to take power it would still be a problem.