You asked about why there has been so much antisemitism in the world and even in the U.S.
A very good question. So here goes.
First a word of clarification. When you asked about antisemitism I believe you were really asking about anti Jewish prejudice. Semites, technically speaking, are all people who share in a common language root, the semitic languages of the Middle East, notably Hebrew and Arabic plus a bunch of ancient languages no longer spoken. But let’s go on and talk about anti Jewish prejudice.
Relations between Jews and Gentiles were tough from before the time of Jesus. The main reason was their insistence on worshiping an invisible God while denying that any of the other gods were even gods at all. Moreover, Rome had a law that all people under its rule could go on worshiping their own gods in their own ways, but they had to worship Roman gods also, at least in a superficial way and on major holidays. Herod the Great was a friend of Caesar and managed to lobby through an exemption for Jews. That did not sit well with other occupied nations who were denied such a deal.
Then along came the Christians, who were seen as some sort of weird Jewish sect, but one that actively tried to convert good, honest pagans, which regular Jews would never do. Things were getting out of control. At about the same time the Jews of Palestine began a series of wars against Rome. It did not go well for them, and in 70 A.D. the Romans had had enough. They destroyed the temple right down to its foundation and burned Jerusalem to the ground. Just to put that in perspective, it was about five years after Peter and Paul were executed in Rome which is about where the New Testament story ends. Anyway, with the temple gone along with all the priests and Sadducees, the only Jewish religious leaders left were the Pharisees. They got together to decide about the best way to go on being Jewish without a temple and all of its rituals. What they came up with eventually matured into modern day Rabbinic Judaism. At the same time they decided on a final break with the Christians since most of them were gentiles and not proper Jews. They didn’t want them worshiping in the synagogues along with real Jews anymore. Over time they prepared a prayer to be recited at each worship service that included a request that God punish all slanderers, and the wording of it was such that any Christian would recognize it as against them. That pretty much ended the Jewish-Christian link.
Remember that I said that the New Testament story ends about the time when Peter and Paul were executed around the year 65 A.D.? Most of the writing of the New Testament, except for Paul’s letters, came after that. John’s gospel, the last of them, was written well after 70 A.D. The split with Judaism had already occurred when John wrote, and you can see it in the words he used. John was a Christian Jew who was ticked off about it.
Now we need to leap forward a couple of hundred years to the early 300s when the emperor Constantine legalized Christianity. Not long after, it became the official religion of the empire. Once again the Jews stubbornly refused to do what Rome demanded. They would not become Christians. That was more or less tolerated until the Roman empire fell apart, the Middle Ages had begun, and poverty, disease, wars and superstition ran rampant all over Europe. Even the Church was increasingly corrupt, and many priests were almost as illiterate as their parishioners. Whose fault? Had to be somebody’s fault! The Jews, those Christ killers, it must be their fault! Look at them! They dress funny! They talk funny! They refuse to worship Jesus, and they do strange secretive things in their services. I’ll bet it’s devil worship! And John’s gospel had a lot to do with that idea.
Jews were prohibited from living where they wanted. They were rounded up and forced to into ghettos. They were prohibited from most ordinary occupations, but, since lending money at interest was prohibited to Christians, and Jewish practice allowed them to lend money at interest to gentiles but not to other Jews, banking became one way to earn a living. That led to making money in other kinds of trade. Since most Jews were literate in at least two languages, it opened up work in medicine, chemistry and other related fields. Tailoring and sewing were also possibilities. Being educated didn’t help. Educated people are often the object of contempt by the ignorant.
During the crusades Jews were randomly slaughtered by Christian crusaders who, on their way to liberate the Holy Land from Muslims, got rid of a few Christ killers along the way. England banned all Jews from living in the realm. Spain and Portugal demanded that they convert or be tortured and executed. Sometimes they got the order mixed up and started with torture before going on to conversion. Jews moved from place to place trying to find a reasonably safe place to live. Poland and Russia seemed like a good bet because there they could also be farmers, and farming was in their blood. That didn’t last long (watch Fiddler on the Roof).
So where did antisemitism come from? From superstition, the need humans have for a scapegoat enemy, the Gospel according to John, ignorant Christian teaching, and the deliberate marginalization of a people forced into roles that could then be demonized. That’s where it came from.
It is shameful. There is no way around that and no excuse to be offered. At the same time, it is important to recognize that any people, nationality, ethnic group or religion can fall into the same trap. We confess that we are a fallen race, and that shows its ugly head anywhere you go. It can be seen in the way Islamic fundamentalists hate things Western. It can also be seen in the caste system of India, the way the Han Chinese marginalize and oppress non-Han Chinese, and, in our own country, how the dominant white population has treated blacks, Indians and other minorities.
What can we, as Christians, do about it? We can love the Lord our God with all our heart. We can love our neighbors as ourselves, remembering especially the significance of the parable of the Good Samaritan. We can love others as Christ loved us. It’s that simple, and it’s the hardest thing we will ever learn to do.