I'm not an expert on the subject but I believe there was a time when it was a husband's right to have sex with his wife and it was her duty to have sex with him! You have to frame this within the women as second class citizens box... or from a male religious basis, the duty to submit, satisfy the man, and oh yes, procreate.
Now multiply that times 4...and you get to buy em if you like/we have this in nations today ---savage nations with modern military as well.