Slavery persisted throughout Imperial history, indeed back at least to the Shang kingdom of the 2nd century BC, but never seems to have assumed the proportions reached under Rome. Slaves were generally relatives of the most heinous criminals, war captives or purchased from traders, though the latter means was of less explicit legality. Various rulers tried to control the practice - who might be a slave, how many may be held, how they should be treated - though there's no clear dynastic pattern apart from Wang Mang's short-lived prohibition of slave trading. The status was officially abolished in 1910, but continued illegally.