It seems like God changes His mind a lot, allowing people not only to marry more than one wife and to divorce them and to marry women taken captive and to have concubines and then saying that this is no longer allowed. I guess that this is a case where there was no objective Truth.
Deuteronomy 21:10-17:
10 When you go out to war against your enemies, and the Lord your God hands them over to you and you take them captive, 11 suppose you see among the captives a beautiful woman whom you desire and want to marry, 12 and so you bring her home to your house: she shall shave her head, pare her nails, 13 discard her captive’s garb, and shall remain in your house a full month, mourning for her father and mother; after that you may go in to her and be her husband, and she shall be your wife. 14 But if you are not satisfied with her, you shall let her go free and not sell her for money. You must not treat her as a slave, since you have dishonored her.
15 If a man has two wives, one of them loved and the other disliked, and if both the loved and the disliked have borne him sons, the firstborn being the son of the one who is disliked, 16 then on the day when he wills his possessions to his sons, he is not permitted to treat the son of the loved as the firstborn in preference to the son of the disliked, who is the firstborn. 17 He must acknowledge as firstborn the son of the one who is disliked, giving him a double portion[a] of all that he has; since he is the first issue of his virility, the right of the firstborn is his.
Deuteronomy 24:1-4:
1 Suppose a man enters into marriage with a woman, but she does not please him because he finds something objectionable about her, and so he writes her a certificate of divorce, puts it in her hand, and sends her out of his house; she then leaves his house 2 and goes off to become another man’s wife. 3 Then suppose the second man dislikes her, writes her a bill of divorce, puts it in her hand, and sends her out of his house (or the second man who married her dies); 4 her first husband, who sent her away, is not permitted to take her again to be his wife after she has been defiled; for that would be abhorrent to the Lord, and you shall not bring guilt on the land that the Lord your God is giving you as a possession.