Why would political or religious leaders espouse anti-Semitic ideas?

The history of antisemitism - defined as hostile actions or discrimination against Jews as a religious or ethnic group - goes back many centuries; antisemitism has been called "the longest hatred".[1] Jerome Chanes identifies six stages in the historical development of antisemitism:

Pre-Christian anti-Judaism in ancient Greece and Rome which was primarily ethnic in natureChristian antisemitism in antiquity and the Middle Ages which was religious in nature and has extended into modern times Traditional Muslim antisemitism which was-at least in its classical form-nuanced, in that Jews were a protected class Political, social and economic antisemitism of Enlightenment and post-Enlightenment Europe which laid the groundwork for racial antisemitism Racial antisemitism that arose in the 19th century and culminated in Nazism Contemporary antisemitism which has been labeled by some as the New Antisemitism[2]

Chanes suggests that these six stages could be merged into three categories: "ancient antisemitism, which was primarily ethnic in nature; Christian antisemitism, which was religious; and the racial antisemitism of the nineteenth and twentieth centuries".[3]

In practice, it is difficult to differentiate antisemitism from the general ill-treatment of nations by other nations before the Romanperiod, but since the adoption of Christianity in Europe, antisemitism has undoubtedly been present. The Islamic world has also seen the Jews historically as outsiders. The coming of the scientific and industrial revolution in 19th-century Europe bred a new manifestation of antisemitism, based as much upon race as upon religion, culminating in the horrors of the Nazi extermination camps of World War II. The formation of the state of Israel in 1948 has created new antisemitic tensions in the Middle East.