Jewish rabbis today are very concerned about "marrying out" and are starting to discourage it more. Then there's the story of Phineas, who when a "mixed" couple (a Jew married to a gentile) appeared before him, killed them both -- from which charming episode the modern "Phineas priest" assassins take their names.
Then there's the story of Solomon and the Queen of Sheba. He married her, didn't he?
The phenomenon of "black Jews" goes back at least to the New Testament: remember how Philip encountered the man on the road who was coming down from Jerusalem, returning to his home in Ethiopia? The man was a treasury official appointed by Queen Kandaka (in the Greek spelling -- we recognize the name in its Latinized form, "Candace": bet Candy Bergen doesn't know she's named for a 2000-year-old Queen of Ethiopia). He was an Ethiopian Jew. They still have Ethiopian Jews. How'd that happen?
Probably interacial marriage. There were different levels of acceptance over centuries. What may have been common in one generation was probably totally unacceptable in another era. Just guessing, though. Just like divorce and polygamy. God meant for man to have only one wife and for life but that isn't followed just like when King David reigned, they had hundreds of wives and thousands of concubines. (Busy man.) But that didn't make it acceptable to God.
One more thing, King Soloman never married the Queen of Sheba. That is a myth. As a matter of fact, nothing in the bible even says they were lovers. She had heard of his wisdom and riches and came to see for herself and to make a long story short. She came, she saw, she asked questions, she approved and went home. Anything else is just assumption and God cautions us about that.