The actual act of taking and placing of persons into "slavery" did not occur in this country. This was not the "scene of the Crime". This country has never conquered a people and placed them into slavery. Any slave which came to this country was in that condition prior to their arrival in this country, and for that matter were in that condition before they ever boarded a ship which brought them here. Even the indentured servants which came to this country as payment for crimes or placed themselves into that situation as payment for their passage to this country, such as my GGGG-grandparents.
Was the Southern states even a cause for the market in a slave trade? NO!
The slave trade existed in the world market place, and was a common place practise, far longer that the American Colonies ever existed and certainly much longer than the United States has existed. And even if that were the case, the Northern Rum trade for sugar, from the Bahamas particularly in Massachusetts and other New England colonies and later, states, was more of a driving cause in the expansion of the North American slave trade institution than was that of the Southern argiculture.