Albert Barnes Commentary 1 Kings 11:2

"of the nations concerning which Jehovah said unto the children of Israel, Ye shall not go among them, neither shall they come among you; for surely they will turn away your heart after their gods: Solomon clave unto these in love." — 1 Kings 11:2 (ASV)

You shall not go in to them... - These words are not a quotation from the Pentateuch. They merely give the general meaning of the two passages prohibiting intermarriage with neighboring idolaters (as noted in the marginal references). Strictly speaking, the prohibition in the Law against intermarriage was confined to the Canaanite nations. But the principle of the prohibition applied equally to the Moabites, Ammonites, and Edomites, who all bordered on the Holy Land, and was so applied by Ezra (Ezra 9:1) and Nehemiah (Nehemiah 13:23).