"...the Atlantic slave trade was very much a British enterprise..."

Oh, crap. About 70% of the Blacks brought to the Americas were bought and sold by the Portugese, who felt entitled to do so by their recent history. They had been enslaved by the Moors from about 711-1492.

Nearly 800 years of Moorish occupation of the Iberian Peninsula changed the appearance of their people greatly. I'm not sure the percent of Arab v. African Black in the mix of Moors, but some were surely Black.

The majority of future slaves went to Brasil, an area that the Portugese thought would propel them into one of the rich and powerful countries of the world.

Spain also had a hand in things. The claimed the area (essentially) east of New Orleans all the way through Florida to the Atlantic. Spain was the second largest trader in the Modern Slave Trade era.