I have a couple of books somewhere, although it's been a decade or so since I last read them. One is this: https://www.amazon.com/Northern-Crusades-Second-Eric-Christiansen/dp/0140266534

Would you recommend anything?

When it comes to that eastern slave trade, a Finn, Jukka Korpela, recently wrote a pretty good book about it, but it's available only in Finnish.

Although the more thorough - and expensive - academic version is in English.

https://www.amazon.com/Karelians-European-9001600-Studies-Slavery/dp/9004447199

I have a couple of books somewhere, although it's been a decade or so since I last read them. One is this: https://www.amazon.com/Northern-Crusades-Second-Eric-Christiansen/dp/0140266534

Would you recommend anything?

When it comes to that eastern slave trade, a Finn, Jukka Korpela, recently wrote a pretty good book about it, but it's available only in Finnish.