Final answer:
The correct word to fill in the blank is 'domestic', referring to servants in the household of their owners in the context of early civilizations' slavery systems.
Step-by-step explanation:
Others worked as domestic servants in the household of their owners. In all early civilizations, prisoners of war, criminals, and debtors could be available for sale. This concept of "people owning people" was pervasive across many societies and time periods, including prominent empires such as those in Africa, Mesopotamia, and Rome, with slaves fulfilling various roles from field labor to more skilled positions like business managers or bureaucrats, depending on their background and their owner's needs. In the household, slaves could perform a broad range of duties, and in Roman society, which was heavily dependent on slave labor, a significant fraction of the population consisted of enslaved individuals. Even freed slaves, known as freedmen in Rome, had limited rights. Overall, slavery represented an inseparable and longstanding aspect of early civilizations and persisted well into the 19th century.