Judges 3:6

And they took their daughters to be their wives, and gave their daughters to their sons, thus entering into the most intimate social relationship with them, and served their gods, the natural consequence of breaking down the barriers which the Lord had erected by His prohibition, Exodus 34:16; Deuteronomy 7:3. That is almost invariably the progress of apostasy: friendship with the world, marriages with infidels, rejection of the Lord.