I think it's basicallly because they wouldn't lie down and they wouldn't assimilate. So many peoples have been annihilated through genocide, persecutions and the fact that they were just gobbled up by a superior culture. In ancient times, most peoples religion was Polytheistic, ie they believed that there were many gods and deities. There were bigger gods and smaller gods. It was usual to honour local gods, even if they were not
your god, because you wouldn't like a gods wrath upon you. These superstitions were common. The Jews were monotheistic, and channeled their superstition away from all deities except one. Naturally, those whose god didn't get respect were a little miffed
The Jews kept their one god through all adversity, and that kept them from being assimilated into greater cultures, such as the Egyptian, Persian and Roman. After the Jews were cast out of Palestine and Judea, they became strangers everywhere they went. And nobody likes strangers, right?
The main difference between the Jews and other persecuted minorities through the ages, is that the Jews are still around. They have a sense of their "Jewishness". Weaker cultures have just succumbed to the pressure.
PS. I find the notion of a Jewish "race" utterly racist and despicable. As far as I'm concerned, The only race that matters is the human race.
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