Slavery in the Old Testament: Female captives of war

Did God approve raping female captives of war? (Deut 21:10-14)

Atheist often use this verse to show others how the Bible condones rape and slavery. But we should know that they are superficial readers who keep some handpicked verses which when superficially read misguide us.

"When you go out to battle against your enemies, and the Lord your God delivers them into your hands and you take them away captive, 11 and see among the captives a beautiful woman, and have a desire for her and would take her as a wife for yourself, 12 then you shall bring her home to your house, and she shall shave her head and trim her nails. 13 She shall also remove the clothes of her captivity and shall remain in your house, and mourn her father and mother a full month; and after that you may go in to her and be her husband and she shall be your wife. 14 It shall be, if you are not pleased with her, then you shall let her go wherever she wishes; but you shall certainly not sell her for money, you shall not mistreat her, because you have humbled her."

and you take them away captive -  According to the war customs of all ancient nations, females weren't killed in the battles but were taken as spoils/ captives. For example, in 1 Samuel 30 Amalekites didn't kill any Israelite women but took them as captives. Whether it was voluntary or involuntary should not be considered as a feature of Biblical slavery because it was a custom. God accepted this custom because he wanted everyone to be saved (Isaiah 45:22-23).

see among the captives a beautiful woman, and have a desire for her and would take her as a wife for yourself,- women captives were often raped and sold as slaves by other nations but it was different with the Israelites, they couldn't have sex with slaves for fulfilling their sexual desires, the verse says that they should have a desire for her and should be willing take her as a wife. 

then you shall bring her home to your house, and she shall shave her head and trim her nails. She shall also remove the clothes of her captivity and shall remain in your house, and mourn her father and mother a full month; and after that you may go in to her and be her husband and she shall be your wife- God enacted that, in the event that her master was captivated by her beauty and contemplated a marriage with her, a month should be allowed to elapse, during which her perturbed feelings might be calmed, her mind reconciled to her altered condition, and she might bewail the loss of her parents, now to her the same as dead. A month was the usual period of mourning with the Jews, and the circumstances mentioned here were the signs of grief—the shaving of the head, the allowing the nails to grow uncut, the putting off her gorgeous dress in which ladies, on the eve of being captured, arrayed themselves to be the more attractive to their captors. The delay was full of humanity and kindness to the female slave, as well as a prudential measure to try the strength of her master's affections.

if you are not pleased with her, then you shall let her go wherever she wishes- if his affection cooled towards her, and all the above methods tended to abate his love of her, then he was obliged to dismiss her, or to grant her her freedom, and let her go wherever she pleased.

you shall not mistreat her, because you have humbled her- by humiliating, disappointing and disgracing as he divorced her, in Israel bethrothal was treated as marriage (Deuteronomy 22:23-24).

During historical periods covered by the Bible, most societies were patriarchal, meaning men held exclusive power with the rare exception of ruling queen. A man was needed for woman's protection and for her economical supports. So women mostly depended on men.