I am the son of Jewish parents who were children of Jewish parents who themselves were children of Jewish parents who were children of Jewish parents. As a fifth generation Jew in this country all of whose direct ancestors were Jewish and who came from Germany, Hungary, Poland, Ukraine, Georgia and Russia I can say with certainty that aside from the occasional individual convert to Judaism, generally, you are originally from the Jewish exile from Israel, and Judea of around 70-135 AD. SOme went north, some went west and a few went east.
There are no mass conversions to Judaism in the last 2000 years. No medievial or earlier families and areas in Europe or Eurasia converted to Judaism. Humans maybe masochists at heart, and a few may chose to be Jewish, but the world has not revolved for the last 5000 years for people trying to be members of the tribe