This was a world in which blood and descent were seen as fundamental... solidarities were central to shaping patterns of property, power, and violence. To people who constantly saw fate and fortunes of individuals determined by their birth and descent, it was natural to conceptualize humanity in similarly genealogical terms
The human classification of the Middle Ages... enabled them to assign status, control movement, and limit agency for groups that they identified as different from, and thus in their view inferior to, their own.