Final answer:
The end of the world, according to the Tralfamadorians in Kurt Vonnegut's 'Slaughterhouse-Five,' is caused by an accidental pressing of a button on a spaceship that triggers an experimental fuel, leading to the Universe's destruction.
Step-by-step explanation:
The Tralfamadorians state that the end of the world is caused by the pilot of a Tralfamadorian spaceship, who accidentally presses a button that triggers an experimental new fuel, leading to the destruction of the Universe.
This scenario is presented in Kurt Vonnegut's novel "Slaughterhouse-Five," where the Tralfamadorians are an alien species with a unique perspective on time and death. The answer to the question is none of the provided options (war, natural disasters, human overpopulation, alien invasion), as the Tralfamadorians point to a more abstract concept involving an accident with a spacecraft.