Big Question regarding a long period affected by a swarm of butterflies. But it's something I've pondered about before.
The first type of slavery in the Islamic world that comes to popular imagination would be that of harems/concubines full of women from many places. Whether something like this would occur without Islam is hard to say. Christian rulers took plenty of mistresses and later in the New World would have sexual relations with slave girls, but not much of the sort happened in the Middle Ages as far as I've found. Further east, there will be Zoroastrian, Buddhist, and Hindu states. I know the former frequently outlawed slavery altogether, but I don't know about the other two.
Next is the enslavement of men and boys, most commonly done to gather mamluks and other enslaved armies. I haven't found any record of non-Islamic states before the conquest or their contemporaries doing something similar. This also had a great effect on both the Middle East and especially India, both of which saw several empires arise founded by Turkic or Caucasian slave soldiers. Of course, the Byzantines and Sassanids heavily employed mercenaries from various bordering lands so it's likely that this process will continue. What this would entail exactly? Again I'm not sure.
Lastly, there's the slave trade itself. This includes the mass enslavement of Slavs that helped bolster the economies of Venice and much of Europe, and also East Africans along the Swahili coast. One also can't forget the Barbary corsairs of Northwestern Africa, who will likely be Western-leaning Christians ITTL, making them far less likely to enslave Europeans. Also, the Vikings are lacking major markets in Al Andalus and Iraq.
From the rough outline of this timeline, it looks like although slavery may be less prevalent in ITTL, many regions may be less economically developed compared to our world at this time.
Have at it.
The first type of slavery in the Islamic world that comes to popular imagination would be that of harems/concubines full of women from many places. Whether something like this would occur without Islam is hard to say. Christian rulers took plenty of mistresses and later in the New World would have sexual relations with slave girls, but not much of the sort happened in the Middle Ages as far as I've found. Further east, there will be Zoroastrian, Buddhist, and Hindu states. I know the former frequently outlawed slavery altogether, but I don't know about the other two.
Next is the enslavement of men and boys, most commonly done to gather mamluks and other enslaved armies. I haven't found any record of non-Islamic states before the conquest or their contemporaries doing something similar. This also had a great effect on both the Middle East and especially India, both of which saw several empires arise founded by Turkic or Caucasian slave soldiers. Of course, the Byzantines and Sassanids heavily employed mercenaries from various bordering lands so it's likely that this process will continue. What this would entail exactly? Again I'm not sure.
Lastly, there's the slave trade itself. This includes the mass enslavement of Slavs that helped bolster the economies of Venice and much of Europe, and also East Africans along the Swahili coast. One also can't forget the Barbary corsairs of Northwestern Africa, who will likely be Western-leaning Christians ITTL, making them far less likely to enslave Europeans. Also, the Vikings are lacking major markets in Al Andalus and Iraq.
From the rough outline of this timeline, it looks like although slavery may be less prevalent in ITTL, many regions may be less economically developed compared to our world at this time.
Have at it.