This novel is classified as part of the post apocalyptic genre why?

I think that McCarthy's masterpiece is poetic, sparse and haunting. He is able to simplify the utter desolation of a post-apocalyptic Earth. We can, from the beginning, see the world has underwent a catastrophe that it cannot recover from. McCarthy doesn't clutter his story with many peripheral characters or unnecessary action. He keeps his story simple and charter driven. There is an emptiness about everything except for the boy and dad. There is no sense of urgency because really it is too late, the Earth is done. The only glimmer of hope lies in the love between the boy and father and within the boy himself, "If he is not the Word of God, then God never spoke .." Everything else is simply empty or rotting including humanity. McCarthy keeps it simple, beautiful and utterly terrifying.