Slaves of Mordor

[Rumil]

I presume the slaves working around Nurnen would be supplied by the Easterlings and Haradrim, perhaps defeated members of sub-tribes of these warlike peoples. I expect they were supplemented by captives taken in raids on Gondor and its allies, as were the slave rowers of the Galleys of the Corsairs, who seemed glad to join the fight against their former oppressors when liberated by Aragorn. I guess any orcs commiting minor transgressions could also have been used as slaves (those comiting major transgressions would surely have been eaten by their compatriots or sent to Shelob!). I wonder if any captive dwarves or elves were enslaved? Morgoth had certainly enslaved elves during the first age. Plenty of Fanfic/RPG potential!