Late again. Sorry.
Deuteronomy 21:10-14 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.
The practice of taking captive women as concubines has long been frowned upon in western cultures, and for good reason. As with marrying more than one woman, marrying a prisoner of war is a complicated and difficult proposition. A man of weak character can’t pull it off, and a man of poor character can’t do it well. On the other hand, difficult doesn’t mean sinful or impossible. In fact, in the context of the ancient near east–probably in other contexts as well–marriage was one of the best options available. It is better than killing her with the rest of her people or leaving her to be abused or enslaved by some other nation. At least as a concubine to an Israelite, she would be brought into the religion of Yahweh and enjoy the rights accorded to all wives by Torah.
Allowing a man to take such a woman back to his home also recognizes and helps to stem the harsh reality of rape in war. This law says that a man is not allowed to simply take whatever woman he wants, but knowing that he can still have her after following the proper procedure (and being reminded of that fact every year when reading Ki Tetzei in the synagogue) can serve to temper his immediate lusts. Chances are very good that after the thirty days of mourning have passed, he will have realized what a crazy idea it is to bring a pagan woman into his house, and he will allow her to leave. If not, then he would be required to begin her education in Torah and her conversion to belief in the True God before he could consummate the marriage. (See Leviticus 19:19, Deuteronomy 7:3, and Deuteronomy 22:9-11.)
If he changes his mind and allows her to leave, she will no longer be a prisoner of war but a free woman with all the rights of a stranger in Israel. Those rights were considerable indeed, especially in light of what she might face in some other land.