Slavery
Slavery is a family of institutions and practices in which people are held under coercive domination. In some systems slavery is openly defined through legal ownership; in others, similar control appears through war captivity, debt, inherited status, household authority, sexual coercion, penal labor, caste, trafficking, migration control, or the practical impossibility of leaving.
The 1926 Slavery Convention framed slavery around the exercise of powers associated with ownership over a person. A comparative history of slavery therefore has to ask which powers attach to the person in a specific society: sale, forced labor, control of movement, sexual access, family separation, inheritance of status, punishment, legal exclusion, or denial of exit.
Comparative frame
Slavery is not one timeless institution. Ancient household slavery, Roman legal slavery, plantation chattel slavery, slave soldiers, concubinage, serfdom, debt bondage, penal labor, and modern forced labor differ in law and social form. They overlap when vulnerability is converted into durable command over another person's body, labor, sexuality, children, legal standing, or movement.
A useful distinction is between stock and flow. Stock is the number of enslaved people present at one time. Flow is the number transported, sold, captured, born into slavery, freed, or killed over a period of time. This matters because a slave society with a large resident enslaved population is not the same kind of evidence as a trade route through which millions of captives passed over centuries.
Evidence and measurement
The earliest secure documentary evidence often cited for slavery comes from Early Dynastic Mesopotamia. A Louvre tablet from Shuruppak/Fara, catalogued as AO 3765, records a transfer traditionally described as involving a male slave and a house, around 2600 BCE. Earlier proto-cuneiform evidence may point to dependent or enslaved people, but it is less secure and should not be treated as a simple birth certificate for slavery.
The transatlantic slave trade is unusually measurable because ship logs, port records, customs documents, plantation accounts, and modern database reconstruction preserve large parts of the traffic. The SlaveVoyages database estimates roughly 12.5 million people embarked from Africa and about 10.7 million disembarked in the Americas. Those figures describe a transport flow, not the total number of people enslaved within Atlantic societies across generations.
Modern antislavery law usually addresses illegal coercive control rather than lawful title in human beings. The International Labour Organization, Walk Free, and the International Organization for Migration use the term modern slavery for categories including forced labor and forced marriage, while keeping those categories analytically distinct from historical chattel slavery.