I would call them conquered, or maybe even vanquished.

For the most part, they were a defeated race of slaves. Only with the advent of the guilds and the merchant class did they really start to become civilized.

People are not civilized if they are considered chattel, they are just subdued, like sheep.

Sheep, that sounds like a familiar moniker.
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The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)