...Does that matter who they were sold by? Seeing as Europeans supplied the market?
And yes,
millions
Again, not really sure how that's relevant.
African slave traders didn't go and round up a bunch of people and then Europe, twiddling their thumbs, came by and went "golly gee whilickers! Well I mean if you already kidnapped them, I
guess we could buy them... As long as you aren't kidnapping them
on our accord..."
They were captured because they knew Europeans and colonial governments would pay money for them, because slavery was a major part of many colonial economies. This is a trade that went on for hundreds of years. Not some one-time cash exchange.