Among other things such as waging war, the islamic doctrine of offensive jihad (holy war) means Allah recommends you to purchase sex slaves. But only if they are non-muslims.
“You go to the market, look at the sex-slave, and buy her. She becomes like your wife, but she doesn’t need a marriage contract or a divorce like a free woman, nor does she need a wali. All scholars agree on this point–there is no disagreement from any of them.”