How does the psychological nature of the mind connect to imperialism?

In Heart of Darkness the author, Joseph Conrad, portrays the ways in which Freudian psychology is interpreted and shown throughout the mind;subsequently, this is shown by the three outposts which Marlow visits in the Congo: the outer station (representing the superego), central station (representing the ego), and inner station (which represents the id).  These were placed by Conrad in order of the most outward appearance being closest to the mouth of the river, the superego, while the inner primal rage resides in the landmass, the inner station.  In the outer station, Marlow meets the Company's chief accountant who is "respected" (Conrad) by Marlow for having "kept up his appearance" in the "great demoralization of the land" in the same way that your superego it the outward psychological portrayal which shows and allows for socially acceptable behavior.  It should be added that though the land is demoralized, it is not classified as primal or brutal.  Marlow's arrival at the central station gives rise to a middle ground of a somewhat acceptable environment with a clear underlying brutal diction. The person who is the metaphor for the ego, the manager, also takes rise from this station and represents the ego as he is ultimately the separator in appearance as he is described as a "commonplace in complexion, in features, in manners, and in voice. He was of middle size and of ordinary build."  This ultimately shows us that he is nothing special and stands on the middle ground between the the respectable appearance of the chief accountant and the obvious primal nature which surrounds Kurtz, who resides at the inner station.  This primal urge is seen from the decapitated heads which remain stationed on spears which reside just outside Kurtz's residence and represents the inner station as a whole.  Though I understand all of this, I find it hard to relate how this psychology can relate or rather to what the psychology points to about the nature of imperialism.  Perhaps it is just a theme in the story which simply points out how the mind manipulatively uses self defense mechanisms and through basic psychological understandings, further emphasizing the distancing which society places emphasis on when faced with imperialism, or perhaps it is a further effect to attempt to mirror the European psyche which is explained as behind the emphasis on outward appearance presented by the superego (which the Europeans approve of) or the primal nature which was expected to be found in the tribes of the Congo, though the tribes are ironically more controlled than the imperialists, as evidenced by the hungry crew of cannibals on the steamboat who refrain from eating the pilgrims on the boat.