Organized hostility to Jews as a religion and people.
It has a long history, since the rise of Christianity (and to some extent in the pre-Christian Roman Empire and the ancient Middle East).
During the Medieval period in Europe Jews were often killed, partly for their greater wealth, partly because they were "different". In Christian cultures hostility to Jews is based on the theory that "Jews murdered Jesus". That is, all Jews were held guilty for the actions of a few people at a specific time (for an act best described as mythical) - this at a time when a horse could be hanged if its rider died due to its rearing up. Norman Cohn's book is essential reading on the history. Also of interest is "Anti-semitism throughout the Ages" by Heinrich Coudenhove-Kalergi, published in 1901 - an Austro-Hungarian aristocrat countering the beliefs of his class. See Israel
The real cause may be the fear of people with different customs. The cure perhaps is to accept that the planet as a whole contains peoples with many different beliefs. There is no reason to believe that any are worse than others, though in a secular state, all can be expected to conform to common laws of decency: no human sacrifice, but otherwise to be treated as voluntary societies where the members consent to activities.
In recent times anti-Jewish massacres have been characteristic of Tsarist Russia, pre-1939 Poland and then Nazi Germany. On the ending of communism there were fears that it might revive in post-Communist Russia and such countries as Hungary, Slovakia and Croatia. These fears have not proved well-founded.
Until the foundation of Israel Jews have usually been tolerated better in Muslim countries than in Christian.
See also racism .
Cohn - Warrant for Genocide
The Myth of the Jewish World Conspiracy and the Protocols of the Elders of Zion
Die Protokolle der Weisen von Zion. Der Mythos von der jüdischen Weltverschwörung
Histoire d'un mythe
Anti-Semitism Throughout the Ages
Antisemitismus. Von den Zeiten der Bibel bis Ende des 19. Jahrhunderts