I know this is a hard question to ask, because you are right it can be inflammatory. But asking it is really important in fighting antisemitism. I'm a grad student in Holocaust studies, and I don't even really have a satisfactory answer. The United States Holocaust Memorial Museum currently has a digital exhibit that may be helpful. But here's some basics if it helps. Antisemitism has been described as 'the longest hatred' it has had many different iterations over time. And it goes back over 2000 years. There are racial, religious, and political forms of antisemitism and often they interact. For example Nazi antisemitism was primarily racial, but it had political parts because it demonized Jews as communists, and it had religious elements because it used Christian antisemitic tropes to further violence against Jews, especially in heavily religious areas who wouldn't be as likely to understand a racial argument for antisemitism.

In areas with a large majority of one religion, particularly one such as Christianity or Islam, which both to some extent require something called supersessionism, the minority of Jews were seen as a threat to their own religious supremacy, and therefore various traditions of violence and demonization were created against them. Supersessionism essentially means that for a religion like Christianity to be true, Judaism must be false. It is a kind of familial or "sibling rivalry" which allowed religious leaders to justify demonizing their Jewish neighbors.

In terms of political antisemitism, in the same way Jews were seen as a threat to religious supremacy, they began to be seen as a threat to political power. They answered to their own communal leaders, and laws, and even though they also followed the laws of the land, they were perceived to have dual loyalty. This is something still seen in modern antisemitism, particularly in the post-1948 accusation of all Jews having a dual loyalty with Israel. It was a political tool which could be used in any system, in a communist world Jews were capitalists, in a capitalist world Jews were communists, and in both worlds, they were Christ-killers.

Racial antisemitism is newer than either of the previous forms, dating back to the 19th century. Racial antisemitism played on previously held beliefs of Jews being demons, as well as the charge of dual loyalties, combined with the observation that Jews were ethnically and socially, as well as religiously and linguistically distinct from their neighbors in most places. As white, Western European philosophers became increasingly interested in defining groups along a racial hierarchy, Jews became a problem. They were seen to be one people, yet they existed in every country, had every skin color. The existence of this group that identified with each other as brothers, yet existed outside the bounds of most racist definitions was seen as threatening. This, along with longstanding antisemitsm coming in other forms lead to defining Jews as racially inferior.

Unfortunatly, none of this really answers the question, 'why the Jews?' It is a tragedy which I belive cannot be fully understood, but I hope this helps.

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