“The conquest of the earth, which mostly means the taking it away from those who have a different complexion or slightly flatter noses than ourselves, is not a pretty thing when you look into it too much. What redeems it is the idea only. An idea at the back of it; not a sentimental pretense but an idea; and an unselfish belief in the idea — something you can set up, and bow down before, and offer a sacrifice to…”
In an almost poetic manner, Marlow presents the basis for which conquerors wreck havoc on those they deem weaker than them. Their actions are based on an idea they have been ingrained with to follow so as not to scrutinize and keep at bay the dark truth lurking underneath.