Most of the union and confederate deaths resulted from

   They did not accept Christianity, the main religion of Europe.

Explanation:  If we take into account that during the Middle Ages religion was the dominant political factor, and given that it was Europe, that religion was Christianity, then all who did not conform to the official version of medieval Christianity were fiercely prosecuted. This also applies to many Christian sects, and of course to Jews who in most cases did not accept Christianity. It must be borne in mind that the Jews are extremely skilled traders and known for their family business and wealth, and this has further created envy among Europeans. That is why the image and propaganda of the Jews as an inferior nation were deliberately created, as the cause of many miseries, primarily historically viewed as responsible for the crucifixion and death of Jesus Christ. There can be seen a bizarre absurdity from the firefighters of Christianity, for if there was no crucifixion of Christ, there would be no resurrection, therefore, there would be no Christianity. But this shows the agony and greed of many European kings, nobles and bishops. The causes of many other troubles were also attributed to the Jews, who therefore experienced massacres during the Middle Ages. Thus, the idea of ​​antisemitism, which in the 20th century had catastrophic consequences, arose. It is a fact that the Jews engaged in borrowing money and taking interest in the name of a loan, which, according to Christianity, was considered a sin. However, this practice was also known to many Christians. The Jews were simply labelled as inferior and even many occupations and jobs were forbidden to them.