… is from pages 125-126 of Thomas Sowell’s 2018 book Discrimination and Disparities (footnote deleted):
If longevity and universality are criteria, then slavery must be among the leading candidates for the most appalling of all human institutions, for it existed on every inhabited continent for thousands of years, as far back as the history of the human species goes. Yet its full scope is often grossly underestimated today, when slavery is so often discussed as if it were confined to one race enslaving another race, when in fact slavery existed virtually wherever it was feasible for some human beings to enslave other human beings – including in many, if not in most, cases people of their own race.