Night of the Living Dead and its counterparts also illustrate the fear of widespread apocalyptic destruction. It is not a coincidence that these movies appeared mostly at the height of the Cold War paranoia that was taking place earlier this century. Much like the atomic bomb, zombies are unleashed in a chain reaction, each devoured corpse arising and looking for more human flesh to consume. As the zombie count increases exponentially, they cover more and more distance until they overtake massive amounts of land area. Consequently, they choose to relocate to an uninhabited island in the tropics as the U.S. becomes a barron wasteland, populated only by the walking dead.
Zombies also represent widespread annihalation in the form of plague-like sickness.
The implications here are basically the same as they are with nuclear apocalypse, but on a more personal and intimate level.