When did the Jews begin migrating all over the known world?
The Jews began migrating all over the then-known world from 606 B.C., during and after the Babylonian captivity. Rather than returning to Jerusalem, they remained scattered throughout the Gentile world, establishing businesses and synagogues in every city of note, eventually throughout the whole Roman Empire.
Les teaches that after the Jews got comfortable in the Gentile world and became astute at banking and business, those who had been out in Babylon began to migrate to every corner of the then-known world. He emphasizes that from 606 B.C. they had been migrating all over that world, and wherever there was a city of any population of note, Jews established businesses and synagogues everywhere throughout the whole Roman Empire. This history explains Acts 2:5, where Jews dwelling at Jerusalem for Pentecost had come from every nation under heaven: when taken out to Babylon, instead of going back to Jerusalem, they scattered throughout the then-known world.