I guess the Jews are the George W Bush of world history.
Old Idea—when trouble exists—blame it on the Jews. Ancient idea, and one that still works so it seems.
The third, which tied in to the above two was in 1793 when Russia swallowed the eastern half of the Polish-Lithuanian commonwealth. Until that time there were few Jews in Russia, while 60% of the worlds Jews or more lived in Poland. The Russians didn't understand this new group and demonised it.
This had the effect of creating a vicious circle -- Jews were marginalized and brutalised (well, most of Russia was) and they eventually moved against this in the late 1800s being drawn to an idea of equality for all -- remember that some, SOME of the earliest socialist ideas are things we now take for granted as equality for all etc. This then influenced the stereotype of the Jew as the "other" and a vicious circle