In the book Silk Roads, their is a chapter that hints at the scale of trafficking and sale of various europeans by various groups such as the vikings and romans. My impression is that this trade was remarkablly lucrative and served as a major economic "good" for trade in history. Is there some hooks out there that focus on this topic? Not just during roman times, but especially following the "fall of rome." During the dark ages what role did tradficing play as a source of wealth for early political power units such as in the one that rose in "france" or other locations which eventually became monarchies in the feudal world?
Silk Roads by Peter Frankopan is a unique combination of lucid writing and broad research. A few books that might strike you similarly, depending on your depth of interest and dedication to the topic:
Marc Bloch, Slavery and Serfdom (1975).
Pierre Bonnassie, From Slavery to Feudalism (1991)
Michael McCormick, The Origins of the European Economy (2001).
Alice Rio, Slavery after Rome (2017).
My general impressions: Bloch is subtle but brilliant, and alas, a bit dated in his concerns (he was executed by Nazis in WWII). Bonnassie is probably more the kind of survey you're thinking of, but he gives an extreme view of the extent of slavery. McCormick casts a very wide net, and his work is rich and encyclopedia-like, which can seem compelling or dense, depending on your own predispositions. Rio is fresh off the press and a similarly thorough scholar, but her read is much more snappy than McCormick's far-reaching work. (Both Rio and McCormick are touchstones for my own research, but you probably won't find either beside Frankopan in your neighborhood bookstore.)
I'd recommend paging through a couple of these online to see if they fit your interest. Then, maybe start with Rio and work your way backwards?