Jews and Slavery in Medieval Ashkenaz

I have always been curious about why European Jews don't look very Middle Eastern. Just read an article that quotes Raphael Patai as saying that the reason why has to do with the medieval slave trade in Europe. His conjecture is that while Jews were prohibited from owning Christian slaves, there was no prohibition against pagans. Jews, especially the Radhanites, were already heavily involved in slave trafficking of Russians and other Slavs, and so it was the case that many Ashkenazic Jews came to own Gentile slaves, whom they needed to help run their households. Unlike the Sephardic Jews who lived in much larger communities and hence could find household servants among Jews, the Ashkenazim had to resort to Gentiles, which in turn introduced multiple halachic problems, such as bishul akum, pas akum, and yayin nesach. In order to circumvent these problems, the Gentile slaves were converted, and eventually, they or their descendants became fully fledged Jews. Likewise, female slaves and their children, were converted and upon manumission became fully fledged Jews without any stigma of geirus or illegitimacy.