After a wave of deregulation policies towards maritime commerce pertaining to slavery, different empires such as Spain, France, etc started to trade enslaved people with one another. Some nations would actually have ongoing wars yet business interests didn’t care about national conflict because profits superseded everything.
Folks assume the US numbers should be higher, but Britain had inter-colonial migrations of enslaved people, as well as France and Spain. An enslaved person, in their lifetime, could have been enslaved in Dutch fort, traveled on a Spanish ship, worked on a sugar plantation in Barbados, and died in upstate New York after serving as domestic enslaved person. I think slave voyages goes by national shop registry, not actual destinations. A slave ship chartered by Britain would go to W.Africa, the islands, and finally stop in the US. Slave voyage would only count Brit, despite the ship ending in the US. Same with France. Le Harve > Martinique > New Orleans. It would only count France.
Lastly, slave voyages is a good resources, but doesn’t fully account for amount of people travelled, nor enslaved in the West African forts. It only counts what THEY put on paper.Piracy and tax fraud is extremely common, and distorts the full numbers of victims.