I'll start things by pointing out that without religion, there would have been no "Gentiles" and no "Jews" in Europe, just people. Religion was and is essential in perpetuating the separate identities.
Two human population groups living in the same place will inevitably mix over time unless they practice cultural separatism. The two religions involved in the history leading up to the holocaust provided that separatism...
Are the "two religions involved" you speak of Jews and Catholics? I think they are. I'm just wondering.
I don't really know what a "Gentile" is. I thought it was a word used by Jews to mean, basically, "non-Jew". But the way your paragraphs were written, the Gentiles themselves could be the entire second religion. I didn't think Gentiles had a religion, they were simply non-Jews. Am I wrong? Or did you simply mean Jews and Catholics and I just don't know enough about history to pick that up?