Though widespread, it is a wrong notion that Islam holds no bar on free sex with the enslaved women taken as war captives. Which specifically mentions Nikah with them after the payment of Mehr. It is like the order concerning drinks which were not strictly banned in the beginning but were later declared unlawful. There are some benefits of drinks but its evil surpasses its benefits. Salat is not valid if offered while under influence of intoxicants.
Intoxicants are unlawful.
Similarly the law regarding captive women can only be comprehended when all the verses concerning them are put together. AND , while AU is for the word OR . In both these verses AU has occurred implying the permission of sex with their wives or the captives they possess. Replace OR by AND in the above and the meaning changes. Till the clear cut order of legitimate marriage with captive women was not revealed, sex without taking them into marriage was not prohibited, which explains the earlier practice and traditions.