Prospective customers of invasion tended to fluctuate with the state of latest affairs, and present perceptions of threat. Alien invasion was a frequent metaphor in US science fiction for the duration of the Cold War, illustrating the fears of foreign (e.g. Soviet Union) occupation and nuclear devastation of the American individuals. Examples of these tales incorporate "The Liberation of Earth" by William Tenn and The Body Snatchers. My websites: Extra terrestrials 2012