Before beginning, it should be noted that when using the term “slavery,” it carries such heavy, evil connotations because one immediately thinks about the slavery that was seen in the West. Islam is no where near similar to the slavery that happened in the west, and a more accurate term to use would be “servant.” In fact, if someone asked what the definition of slavery is, they would say a system where people are forced to work without any rights, compensation, freedom, or way to get out. However, if that is the definition of slavery, then there is absolutely no such thing as slavery in Islam. However, for argument’s sake, the former will be used.
Lawrence Keeley wrote a book called War Before Civilization where he explains how premodern war was primarily about man power; the side that had the largest army was usually going to win, and if an army was few in numbers, they were an easy target for another army to attack and benefit from them. This is why, as Keeley explains, women were very valuable in premodern civilizations because any society’s ability to reproduce and build up this necessary man power is limited by the number of fertile wombs that society has. Keeley says in his book, “Although the loss of even a large percentage of males will have no direct influence on a group’s demographic fortunes (whatever the effect on its military viability may be), the loss or gain of fertile women can mean the difference between population decline and growth.” This is why Keeley argues that all premodern civilizations took concubines, as this was a necessary aspect of war and life. If you didn’t take concubines, your society would be at a major disadvantage militarily, because you can either take concubines, or your people would get wiped off the face of the earth; there was no third option. This is why taking concubines was not only morally justified, but it was morally necessary.
Although what is noted above is enough for this argument, it is still worth mentioning that The Sharias rulings on how to capture and treat slaves/concubines in general are the most humane out of any other civilization. First of all, the only way to capture a slave in Islam is through captives of war. Therefore, you can never make a free man or woman in Islam your slave, as scholars have said that the origin of a human is to be free, as Allah created our father Adam AS as a free man. It is also never based on race, sex, or ethnicity. Rather, slaves can only be obtained through a full pledged war. If one just ponders over this ruling, one can see so much wisdom that comes from it. In Islam, there are different options after war, based on the needs of the community. For example, the captives of wars can be let go, ransomed for money, killed (since they came to kill you too), exchanged for other prisoners, or taken as concubines (for the females). Therefore, in Islam, in caters to such a system where after a war when there is so many losses from both sides, there is a way to regain what it has lost. This is why one can see that all premodern civilizations had to have slaves; it was just a necessary aspect of life in order to survive. However, the vital difference that cannot be overlooked is that slaves in Islam cannot be beaten, mutilated, killed, or prostituted. They have to eat what you eat, be clothed with what you cloth yourself with, not overworked, etc. This system is no where near close to the slavery that we know and think of when we hear the term slavery. For example, if one did beat his or her slave, the Prophet Muhammad PBUH said that the expiation is to free that slave (Sahih Muslim 1657). It was narrated that one of the Prophet’s PBUH companions, ‘Uthman ibn ‘Affan, tweaked the ear of a slave of his when he did something wrong, then he said to him after that: “Come and tweak my ear in retaliation.” The slave refused but he insisted, so he started to tweak it slightly, and he said to him: “Do it strongly, for I cannot bear the punishment on the Day of Resurrection.” The slave said: “Like that, O my master? The Day that you fear I fear also.” In Islam, slaves are guaranteed food and clothing like that of their master’s. It was narrated that when ‘Abd al-Rahman ibn ‘Awf walked among his slaves, no one could tell him apart from them, because he did not walk ahead of them, and he did not wear anything different from what they wore. It was also narrated that one day ‘Umar ibn al-Khattab passed by and saw some slaves standing and not eating with their master. He got angry and said to their master: What is wrong with people who are selfish towards their servants? Then he called the servants and they ate with them. Moreover, slaves could buy their freedom from their master, they have to be treated in a kind and just manner, and they even sometimes had precedence over free men in some matters where that slave excelled in a religious or worldly affair over the free men. For concubines specifically, if she gives birth to her master’s baby, the baby is free. On top of that, she is also freed automatically when her master dies. These rules ensure that captured slaves in Islam would quickly be able to achieve their freedom, especially after one or two generations. Even in Islam, it is a honorable deed if someone freed a slave that they had out of their kindness, and this was encouraged for the Muslims to do. Contrast this to other societies in history that maintain a permanent, subjugated, and unjust slave class based on race or ethnicity, Islamic slavery is not like that. This is why one can see, for example, the Mamluks, who were a ruling class of Muslim slaves and the descendants of slaves, were given such power and duties, some of who even reached the level of Sultan’s and Amir’s in the Muslim Caliphate.
This is why it is very clear from history and objective statistics/arguments that concubines were necessary and that the Sharia was able to preserve families, marriages, and the community as a whole in this way. This is why you see that any premodern civilization would have to have concubines, including even Prophets in the Old and New Testaments. On top of all of this, when one looks at the rulings set in place by the Sharia on how to treat slaves, it is incredibly fair and just with no oppression being involved.
To conclude, it should be noted that in Pre-Islamic Arabia, they used to bury their daughters alive, as having a daughter was seen as a disgrace. Women were treated as property with no rights at all. Even in the western world, women were deprived of many of their rights until recently, such as voting. Islam liberated the women, gave them honor, dignity, and their due rights. This is why, despite all of these outrageous, ongoing allegations against the way Islam treats women, most people who convert to Islam are in fact women!
And Allah knows best.