The Holocaust: Some Germans believed that after a WWI loss, that the Jews were to blame for it. Adolf Hitler was one of them. He built on that idea after coming to power and convincing almost the entire German population this was true. Since he grew in Vienna, Austria, there were a lot of the people were anti-semitic, so he believed that as well. Which led to the concentration camps, and death of millions. Also, generally when there is a catastrophic disease somewhere, they try to isolate as much as possible to keep it from spreading and eventually let it die out and go away. That is what the Nazi's tried—and almost did—to do. They got every European Jew they could get their hands on and force them into camps where they would die off. So this shows how Jews were almost like a disease in how they were nearly treated like one, except they weren't trying to be cured, they were being killed.
Late BC and Early AD: The Jews were disliked even before the crucifixion of Jesus. In 597 BC, Jerusalem was attacked by the Babylonians led by King Nebuchadnezzar. This siege resulted in the destruction of the First Temple, which led to the construction of the Second Temple, which was destroyed 767 hundred years later. Jewish people were also blamed for the crucifixion of Jesus, one of the most important people in Christianity. Since (The Roman Empire, Middle Ages Europe, 1900's Europeans, the Nazi's) most of Europe was one form of Christianity or another, Jews were despised for the crimes committed by their ancestors. It was also believed by some that the Jewish people had too much economic influence.
Rome: The Jews were even disliked by the Romans during their empire ages. They were hated because the Romans were mostly Catholic, which is a branch of Christianity. They were even disliked so much that the Romans invaded Jerusalem and destroyed the Second Temple.
Europe from 40 AD-1948: Many people in Europe disliked Jews so much, they didn't technically have a state for thousands of years. From about 40 AD to 1948 (the founding of Israel), the Jewish people had no real place to worship in mass quantities. People believed, that since the Jewish people had no true state, they couldn't grow in power as much as they used to, showing that Europe had a strong dislike for the Jewish people. Jewish people were also seen almost like African American slaves during the 1800's and 1900's. They weren't emancipated in France, Greece, Great Britain, Italy, Germany, or Norway until between 1791-1891. Which shows that since most people were used to treating Jews unfairly for generations, it was hard to just completely flip around and treat them as normal citizens, much like African American slaves in the U.S.