Reading Empire of the Petal Throne again has me thinking of slavery in Athanor. Slavery is common in much of Athanor, particularly among the Alemanians Mal'Akkans, and Throon. Among the Duma, slaves are only taken as a result of defeat of an enemy in war, and among the Ghul, slavery is unknown. If you are not a person, you are food. Slavery would be a fate worse than being food.
In Zamora, slaves are mostly kept as a result of resolving criminal charges (to pay weregild for someone slain, for instance), as a result of war (captured enemies often become slaves), to settle sufficiently large debt (indentured servitude), or as purchase from another nation that keeps slaves. While slaves are often chattle, slaves do not share a common racial heritage, and the trade of slaves is more like the ancient Mediterranean than the American south. There is not Triangle Trade in Zamoran slaves, nor are airships of slaves carried into Zamora.
Not to say this isn't an unsavory world. Household slaves are much like household slaves in ancient Greece, but slave laborers, prostitutes, and gladiators expose the unsavory side of owning people as chattle. Slaves do work that it is hard or impossible to get freed men to do, and there are escaped slaves who rebel against the yoke of domination.
Thus, it is possible to purchase pack slaves, torchbearer slaves, cooking slaves and the like to serve a party, and such slaves often accompany expeditions into dangerous places where it would be hard to hire a crew of workers to support an expedition.