Antisemitism is the term used when people are prejudiced against Jews just because they are Jewish. Antisemitism is a modern racial term that was invented in 1879 by a German journalist called Wilhelm Marr. However, anti-Jewish feelings are much older than that.
About 2,000 years ago, Jesus, according to the story in the Gospels, was executed for treason. He was crucified, which was the Roman method of execution. Christian teaching did not blame the Romans; it blamed the Jews. As his followers later regarded Jesus as God, so killing him became known as the crime of ‘deicide’ (killing of God). This was the basis of Jew hatred.