Avatar shows the destruction of imperialism clearly. The Na'vi can be seen as the native americans. The americans tried to get what they wanted through force, when the Na'vi doesn't get tricked into letting the americans get the unobtanium.
Just like when the African tribes united to stop the Europeans, Jake Sully and the Na'vi went to the other clans to look for help in stopping "The Sky People," or the Americans.
European Nations fought over African Territory for raw material. The Berlin Conference is where they drew dividing lines for Africa without considering natural the borders. African tribes then united to fight the European rule, but failed due to conflicts between the tribes.
Imperialism in Africa began in the 1870's when the Belgian king sent emissaries to trade with the African natives in the Congo. This act started imperialism as other nations of Europe joined in to claim land.