Did people from the northern ten tribes move into the southern kingdom before the Babylonian captivity?
Yes. Many from the northern tribes migrated south into the southern kingdom before Babylon’s invasion. Consequently, the Babylonian captivity involved not merely Judah and Benjamin but people from all twelve tribes, because those northern migrants were taken captive along with the southern kingdom.
Les explains that even though the Assyrians took many northern Israelites captive into Syria, they did not all remain separated or lost. He teaches that many of them migrated down into the southern part of Israel, so when the Babylonians later came, they would take those people captive as well. Therefore, it was not only two tribes going to Babylon; it would be all twelve. He points to 2 Chronicles 13 and suggests studying Kings and Chronicles for further detail.