Every day, goblins died of old age. Compared to humans and other creatures, goblins had a much shorter lifespan. After their brief youth and longest period of adulthood, they quickly approached death.
Upon death, goblins first attempted to transform into Black Knights, and those who couldn't be transformed were simply thrown into the Demon Pool to become Demon Worms.
In life, they toiled for the Demon King Territory, and in death, they became materials of flesh and blood.
This was the meaning of the Demon King's "slaves." In contrast, in the empire, while peasants didn't have enough to eat or wear and were continuously exploited and persecuted, at least after death they could be wrapped in straw mats and buried in pits.
More well-off civilians could have a gravesite and descendants to pay respects. Which side was better? That might be up to individual interpretation.
