There is a slander going around the internet that has existed long before the internet, which is that the modern Jews in Israel are not real Jews; that they are really the Khazars who converted to Judaism, then migrated into Europe as the Ashkenazi Jews, then later they formed the nation of Israel today.
Jews lived throughout Europe before they were expelled, then throughout North Africa and the Middle East, even in Persia. Khazaria was located north and northeast of the Black Sea and existed for about 5-600 years, to some time in the 13th century when they were pushed west by invaders.
Some years ago I was reading a large secular history book and it mentioned that some Jews traveled north to trade with the Khazars when the Khazars mentioned that their ancestors came from Israel and asked about their original religion.
So when the Jewish traders returned home they sent Rabbis to Khazar to teach them about their original religion. So they converted en masse to Judaism because they were, after all, some of the lost 10 tribes of Israel who were taken away to Assyria and never returned, they went north.
Then shortly after that, I heard about the slander being made against the modern Jews. I now wish I had made a note of which history book it was, but I did not think it was important at the time. It was also a thick book, so it would be difficult to find the story, but it makes perfect sense.
So do not believe the slander being made against the modern Jews, the Khazars were some of the northern tribes.