In the movie, it's Prawn against Human-- i.e. world government against unified dissent. By eliminating the literal, alien part of the story, one might see that the Prawns are symbols for human dissenting classes, or insurgents, or freedom fighters. MNU is the symbol for private world government.
District 9 offers insight in such a coming conflict because it explores the relationship between the Prawn and our real world refugee crisis management practice. Introductory parts of the movie show the Prawns and MNU (a private military firm, or PMF, called Multi-National United) which acts as a PMF that specializes in multi-national, humanitarian aid). The Prawns become refugees and the MNU is the humanitarian firm contracted to build a living space for the refugees, and later to provide security for the humans who surround the district. By using a documentary-style approach to storytelling, it is implied that the film stresses a theme: the media and other organizations often paint refugees as a social problems-- documentaries made over the recent decade have examined similar topics. Rather than solve the problem of a refugee crisis, supranational societies-- the UN or MNU-- delay the problem by way of containment and do little in providing a solution, containment practice, or quarantine, and no effort for re-integration.
Another theme derives from the film's protagonist, Wikus. The accidents he makes in the film causes him to undergo metamorphosis. As he starts to change into a Prawn, he also undergoes a metamorphosis of his identity. He goes from working for MNU (opposing the Prawn) to a subvert, or insurgent, fighting against the MNU in his interest to become human again, return to his love, and live peacefully. The film's grand, romantic idea is that identity changes, injustices are made by private world governments, and conflicts are inevitable, lest not forget technology's role in driving relations of private military firms, MNU.
These thematic parallels to our society are not literal, just possible implications of our future. And, viewers do not see a theory for the future play out in the plot. Rather, while watching the plot develop viewers might associate a private role in future world government because of the futuristic tone that the film utilizes. Even though the Prawns came around 1982, and Christopher
(the Prawn) leaves with his son 20 years later (2002) to begin work that will save his people, this does not mean that the ideas associated with the film's themes are null and void. It means, that private world government is a theme that the film uses.