From the the era Exodus God is so much concern of morality and even given the Israelites to maintain purity. God also instructed them not to take girl from other tribes or clans. If God is so much concerned for purity then why He gave advice of this to His people that "after sleeping with a virgin to make his wife and to let her go anywhere she wish, if they want her no more" (Deu 21:13-14).
(10) When thou goest forth to war against thine enemies, and the LORD thy God hath delivered them into thine hands, and thou hast taken them captive,
(11) And seest among the captives a beautiful woman, and hast a desire unto her, that thou wouldest have her to thy wife;
(12) Then thou shalt bring her home to thine house; and she shall shave her head, and pare her nails;
(13) And she shall put the raiment of her captivity from off her, and shall remain in thine house, and bewail her father and her mother a full month: and after that thou shalt go in unto her, and be her husband, and she shall be thy wife.
(14) And it shall be, if thou have no delight in her, then thou shalt let her go whither she will; but thou shalt not sell her at all for money, thou shalt not make merchandise of her, because thou hast humbled her.
Deuteronomy 21: 10-14 KJV