In the case of Scotland and Spain, yes they traded from Africans, so in this case, blacks who were at the mercy of Scottish and Spanish slaveowners have only themselves to blame for selling their own to the Scottish and Spanish. But in the case of England and Denmark, it wasn't a trade. It was conquest and theft and kidnapping. They were so bent on domination that they couldn't help themselves, and thought it was OK to kidnap black people and enslave them. Sweden did this too.