While I thank you for your input please keep in mind this is a fictional version of our world. In this world slavery in Europe was never abolished, the relevant policies by the different countries you have mentioned never came into being. The institution of slavery in this world isn't out of the blue, it's been there for a long time and was never dead. The main changes in slavery throughout history in this world are the peoples who are being enslaved.

Plus this is a setting for an adventure story, I'm not a historian, nor am I a sociologist or expert on slavery. Just a history enthusiast who wants to create an adventure story that I can enjoy with some like minded people.