How will the world end? (conventions of post appocalyptic genre)

The post apocalyptic genre is a sub-genre of science fiction and focuses around the annihilation of human life. There are many different causes to an Apocalypse in films but popular causes include zombies, nuclear war, a meteor striking the earth or a biblical apocalypse examples of these apocalyptic causes are:
 The war of the worlds


 The war of the worlds is an example of an alien caused apocalypse with invaders coming to earth in an attempt to exterminate the human race.




I am legend 
I am legend is the story of Robert Neville and his continual survival after a failed cure for cancer leaves the world at a standstill when humans start to mutate into creatures that are burnt with uv light and are driven by primal instinct