America was one of the last Western nations to end slavery. By the time slavery came to an end in the USA the only other nations in our hemisphere that had legal slavery were Cuba and Brazil. While there were a few confederate diehards who moved to Brazil after the civil war and there were many Southern Americans who demanded Cuban annexation in order to expand slave territory, I have never seen any evidence of Americans trafficking slaves out of the United States. I'm pretty sure that this may have also been illegal under the 1807 law that officially ended the intercontinental slave trade.

That said, as slavery was banned state-by-state in the North in the early 19th century slaveholders did sell people who would have been emancipated to states where slavery was still legal. Gradual emancipation laws in many states forbade these actions but they were routinely flaunted. Sojourner Truth lost one of her sons to illegal slave trading of this sort, for instance, and proto-abolitionist groups like the New York Manumission Society used legal resources to prevent these kinds of activities. source: Sojourner Truth: A Life, A Symbol by Nell Painter. David Ruggles: Abolitionist by Graham Russell Gao Hodges