At the end of the 19th century Frederick Engels called anti-semitism "the socialism of fools".
You're poor, you're exploited, your life is miserable - so blame it on another group, the vast majority of whom are also poor, miserable and exploited, in the case Engels was talking about, the Jews. Who can benefit from this except the exploiters? It's exactly the same in Britain today with all the hatred being stirred up against 'asylum seekers', or Asians, or blacks - a hatred that has burst out into 'race riots' in a number of northern towns.