"They were dying slowly--it was very clear. They were not enemies, they were not criminals, they were nothing earthly now,--nothing but black shadows of disease and starvation, lying confusedly in the greenish gloom. Brought from all the recesses of the coast in all the legality of time contracts, lost in uncongenial surroundings, fed on unfamiliar food, they sickened, became inefficient, and were then allowed to crawl away and rest."

Identify the theme of this excerpt from The Heart of Darkness, by Joseph Conrad, and explain the author's interpretation of the British Empire.