I've noticed historically speaking the Jewish people are often the target of scorn. I can make sense of contemporary hatred as it seems rooted in evangelicalism, however, why would for example, the Argentine Military Junta pick the Jewish people as representative (to some degree) of the "Marxist threat"?
Is it more often the case this is religious discrimination or ethnic discrimination?
Asking as a non-religious person.
While you wait, you may want to check out the section on Jews and Judaism in the FAQ. Several answers there relate to antisemitism and persecution of Jews.
Pre-Roman discrimination against the Jewish people is fairly straight forward (they were conquered and enslaved because they were neighbors to more powerful peoples e.g. the Babylonians). Romans discriminated against Jews because they conquered Jewish lands and viewed the Jewish people as weak for being conquerable. While the Romans can broadly be described as cruel to the peoples they conquered, they looked down upon the Jewish people more so than they did other groups. The Romans identified the "lack of a God in the Temple" as a point of ridicule and Gaius Caligula put a statute of himself inside the Temple as a way of mocking the Jewish people. This incident, combined with a couple notable acts of rebellion put Jews living in Rome under greater suspicion and discrimination than other conquered peoples.
When Paul began his ministry to the other nations (the idea of "gentiles" is actually a more modern idea; Paul used the term "ethne" or nations in his writings instead), he attempted to bring representatives of the other nations (i.e. gentiles) into God's Kingdom (Israel, specifically Jerusalem) to fulfill an old Jewish prophecy. This is not necessarily the place to get into the theological explanation of that, but essentially Paul viewed Jesus' crucifixion as a means of allowing non-Jews the space to be part of God's children alongside the Jewish people. Paul, being Jewish himself, viewed Jews as the first children of God but thought that Christ-following gentiles could be God's second children.
This idea of being second to the Jews did not sit well with Roman Christ-followers. Paul spent much of his ministry trying to explain this theological point and the letter to the Romans centers on the idea of trying to address the gap between the Roman Jews and the Roman Christ-followers in the city. In part because of this, Romans is the longest Pauline argument we have record of. Meanwhile, the Christ-following gentile writers who disagreed with Paul began developing the Christian canon and they viewed Jews as an afterthought or deliberately excluded them. Despite Paul, Jesus, and essentially every named character in the Gospels being Jewish, a distinctly anti-Jewish narrative arose and we are left with scenes like Matthew 27:24-25 where a Jewish crowd acts as a stand-in for all Jewish people in crying out "his blood be on us and on our children!"
The idea of this "Blood Curse" would follow the Jewish people up to the modern era. Despite Jesus being murdered via capital punishment by the Roman state, many Christians would/will claim that Jesus was killed by the Jews. Some Christian theologians and historical scholars (Rita Botwinick and Willie Jennings) claim that the idea of antisemitism is so central to Christianity that Christianity cannot be separated from antisemitism without making Christianity unrecognizable. This blame for Jesus' death and the subsequent animosity towards Jews was compounded during the medieval era when Christian rulers began importing Jewish people to be used as a forced banking class. Essentially, wealth was considered a grave sin at the time and Christian theology forbid charging interest so wealthy Christians used Jewish bankers as moral scapegoats to charge interest and to be held morally liable for the accumulation of wealth. Being the bankers of this era did not mean that Jewish people lived well; rather, the opposite. They were viewed as property and routinely ostracized and killed. Despite the poor conditions Jewish people lived in, jealousy festered among the poor Christian communities. The grass is always greener I suppose.
Stories of Jews ritualistically sacrificing and eating children to mimic the Christian sacrament of the Eucharist emerged and flourished throughout small villages around this time. Despite the Vatican refuting every single one of these stories as made up nonsense the damage was done and the myth of blood libel has persisted to this day. One thing of note about the myth of blood libel is that this same charge was leveled against early Christ-followers as well. The idea of outsiders eating your babies is a common charge to stir up hatred of the other so I do not believe that the details about blood libel are important or relevant here. What is important is that this myth has stuck around.
For a short time, Christian theologian Martin Luther was not antisemitic. He believed that Jews were Jews only because they had not heard about Jesus; however, upon being told that Jews did know about Jesus but that they did not care, he quickly became antisemitic and wrote On the Jews and Their Lies.
u/rotenKleber has already linked a good comment the perceived link of communism and Judaism, but I would just highlight the lack of theology in the comment. Antisemitism in the context addressed here is not based on religion. "Anti-Semitism" was not a term until the late nineteenth century when the word "Semite" was coined in Germany as an ethnic marker for Jews. The origin of the word "Semite" is actually a central piece of the argument between the use of "antisemitism" and "anti-Semitism" with many Jewish scholars and activists arguing to use the former because "anti-Semitism" is itself a term rooted in the exclusion of Jewish peoples.
The answer to your question is yes.
While I would argue that the root of antisemitism is religious (Caligula's discrimination was rooted in a form of religious oppression and early Christ-followers' rejection of Jews used religious rhetoric to justify the exclusion) many people have also discriminated against Jewish people for non-religious reasons. The bigoted idea of blood and soil precluded many Jews from citizenship in America and Europe until the 20th century and the American census only began categorizing Jews as "white" in the last forty or so years. Many gentiles also discriminate against Jews because of the "Blood Curse." Many Christians wrongfully hold all Jews responsible for Jesus' death and Paul's letter to the Romans has been mistranslated and misused in more ways than I can count to support unspeakable horrors in Christ's name.
While the books do lean a bit more theological in places than historical, I cannot recommend the books Paul was Not a Christian (Pamela Eisenbaum) and The Arrogance of Nations (Neil Elliott) enough for more information about this topic.