I had to write that paper during my Advanced Placement American Lit class senior year of high school.
I can't remember any specifics though...
Perhaps compare the "not with a bang but a whimper" to how the exploitation of the local populations and environment was slowly destroying the area.
"The horror" could in fact be the notion of men without conscience, much like Eliot's "hollow men" who are "stuffed with straw" as they lean on each other for support. However, how much support can equally insubstantiative companions offer?