An older analysis of the Atlantic slave trade was modeled on the so-called triangular trade. This described a system where a ship left Liverpool, for example, with trade goods for Africa, picked up slaves, crossed the Atlantic, deposited the slaves in Jamaica, and took sugar back to Britain, completing the triangle. Several variants of this model existed, of course, and it fits a logical assumption, but the triangular trade mechanism was simply one of a number of ways that commerce worked. By the eighteenth century, slave ships were being designed to carry slaves and little or no other cargo. Nearly two-thirds of those ships were engaged in a simple return sequence, from Africa to America then “deadheading” (sailing empty or near empty) back to Africa. As it grew in scale, the slave trade was less an adjunct to other commerce and increasingly a specialized system.
— Eric Nellis, “The Atlantic Slave Trade,” Shaping the New World: African Slavery in the Americas, 1500-1888, pg.30