I may be late to the game in learning this, but I found out in Nehemiah 11 that 10 of the tribes of Israel never returned to Jerusalem and are pretty much lost to this day. Think about the only two people associated with tribes in the New Testament: Jesus from the tribe of Judah and Paul mentions he is from the tribe of Benjamin. Where are the other 10 tribes? In case you are ignorant like I was, here is a little recap of what happened.
After Solomon dies, his son Rehoboam makes a pretty ridiculous decision. The Israelites ask him if he is going to be easier on them than their father. Instead of appeasing them, Rehoboam institutes forced labor and says in 1 Kings 12:14 “My father disciplined you with whips, but I will discipline you with scorpions.” I don’t think that statement would go over well for any ruler ever in history. This causes 10 of the 12 tribes to split and form the northern kingdom which becomes known as Israel. The remaining 2 tribes are Judah and Benjamin who form the southern kingdom to be called Judah. Also important is that Jerusalem and the temple were located in Judah.
Since Israel (the northern kingdom) didn’t have their own place of worship, they created their own places to worship and elevated 2 golden calves to the status of gods (1 Kings 12:25-33). These worship spots became known as the high places. As punishment God sent the nation of Assyria to capture and take captive the northern kingdom (2 Kings 15-17). The Assyrians force them them out of the promised land into exile in other parts of the Assyrian empire.
Judah, even though they had a temple, opted to follow in the footsteps of their brothers to the north and worshipped idols as well. The Assyrians invaded and gave Judah quite a bit of trouble, but God didn’t allow them to completely drive Judah out mainly due to the faithfulness of Hezekiah. After Hezekiah dies though, Judah turns even worse to the point where they didn’t even know that the Torah existed. So God sends the nation of Babylon, who had just defeated the Assyrian army, to invade and exile the people of Judah (2 Kings 25).
So now at this point there are virtually no Israelites living in the promised land. The 10 tribes of the northern kingdom were scattered throughout the Assyrian Empire, but it was then defeated by the Babylonians. The 2 tribes of the southern kingdom are now exiled out into the Babylonian Empire. The only Israelites who seem to be remaining in the promised are a few of the poorest people of Judah who the Babylonians allowed to stay (2 Kings 25:12). Ironically in the northern kingdom the Assyrians had resettled it with foreigners who began to worship God (though not exclusively) after He sent lions to kill a bunch of them (2 Kings 17:24-41).
Fast forward a few years and the Persian empire now has defeated the Babylonian empire and controls the fate of the Israelites who were exiled. Ezra and Nehemiah go about rebuilding the city of Jerusalem and the temple, but only two and a half tribes are now present. If you read Nehemiah 11, you’ll see only Judah, Benjamin and Levi mentioned because they are the only ones to return to the land. Levi is only counted as half because the Levites were scattered throughout the northern and southern kingdom in cities dedicated to them. This was so they could have a presence all over the land to carry out their priestly duties.
The obvious question now is what happened to the 10 lost tribes of Israel. In 2 Chronicles 30, we do see that at least some people from the northern tribes had escaped the Assyrian exile and found their way back to Israel. They still choose to ignore the need to worship God in Jerusalem at the temple. There were probably very few of them left and they are likely ignored for the rest of the Bible because of their refusal to worship God. The only other mention of one of those tribes comes in Luke 2:36 where the prophetess Anna is said to be part of the tribe of Asher.
So what happened to them? It seems likely that they were just assimilated into the populations of the Assyrian and Babylonian empires. There were a few who returned and probably lived in the promised land, but by the time of the New Testament the Romans had come and built roads leading to more dispersion. Any Jews left would have been scattered after the Romans war with the Jews in the first century.
There have been many wilder theories. One Portuguese guy in the 17th century claimed they were all living in South American when he traveled there. There have been random people groups all over the world who claim to be descended. The current nation of Israel has even declared some of these people groups legitimate enough to have the right to return to Israel and live there. There are even crazier theories that say the Japanese and Irish are actually just descendants of these 10 tribes. I’m not sure how that even makes sense.