And they took their daughters. — This beginning of intermarriages shows that we are now a generation removed from the days of Joshua. Such marriages had been forbidden in Deuteronomy 7:3. but are not among the sins denounced by the Angel-messenger at Bochim (Judges 2:1).
Related Commentaries of Judges 3:6
Judges 3:6
6 And they took their daughters to be their wives, and gave their daughters to their sons, and served their gods.