 This type of invasion usually emphasizes common fears during the Cold War, with the Communist agents suspected everywhere, but has also become common during any time of social change and unrest.This theme has also been explored in fiction on the rare occasion.With this type of story, the invaders, in a kind of little grey/green man's burden, colonize the planet in an effort to spread their culture and "civilize" the indigenous "barbaric" inhabitants or secretly watch and aid earthlings saving them from themselves.