Resurgence of the Sassanid Caste System in Medieval Iran, and its influence upon Hanafi Law.
Instances of caste systems in the broader Islamic world (Arab, Iranian and Afghan)
Much of this comes from Gorbineau and Lindholm, the latter I can vouch for.
Beyond the Islamic world, there's the feudal caste system in Japan (with the Burakumin treated as untouchables), as well as similar systems in other East Asian countries. In Europe, the Cagots were treated as untouchables until the late 19th century.
TIL North Korea instituted a caste system based on a Communist-Confucian framework in the 60s.
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