Post-apocalyptic fiction refers to a type of fiction that is set in the near to distant future. The story is about the world (civilization) after some kind of disaster ruins the world. The disaster might be natural. Something like climate change, crazy volcanoes, or some kind of huge asteroid are all common world destroying scenarios. The disaster could be man made too. More often than not, it is a nuclear holocaust.
"By the Waters of Babylon" is post apocalyptic literature because it takes place in a future that exists after some disaster has killed most people on the planet. The disaster that the story mentions is most likely a nuclear war. Early in the story, John mentions "The Great Burning" and that touching metal can lead to death. A nuclear bomb incinerates just about anything within the blast radius and irradiates metals for years to come. The best evidence John provides for a post-apocalyptic nuclear disaster occurs when he envisions the past and sees the destruction.
Then I saw their fate come upon them and that was terrible past speech. It came upon them as they walked the streets of their city. I have been in the fights with the Forest People—I have seen men die. But this was not like that. When gods war with gods, they use weapons we do not know. It was fire falling out of the sky and a mist that poisoned. It was the time of the Great Burning and the Destruction. They ran about like ants in the streets of their city—poor gods, poor gods! Then the towers began to fall. A few escaped—yes, a few. The legends tell it. But, even after the city had become a Dead Place, for many years the poison was still in the ground. I saw it happen, I saw the last of them die.
Fire and poison mist from the sky is exactly what a nuclear bomb would do. The poison is the radiation poisoning, and it can stick around for decades.
The story is post-apocalyptic because something terrible has happened that they call the Great Burning.
Since they call this event the Great Burning, we can imagine it was some kind of nuclear holocaust. Also, they refer to looking for metal in the Place of Gods. Eventually, the reader learns that the Gods were us, and the place John is going to is a city.
It is forbidden to go to any of the Dead Places. … It is forbidden to cross the great river and look upon the place that was the Place of the Gods … It is there that spirits live, and demons—it is there that there are the ashes of the Great Burning.
This is how we learn that John is a in a post-apocalyptic world, where there were once humans living in houses and cities like we live in today. He talks about priests like his father going into the houses to search for metal and seeing bones that are turning to dust.
After a time, I myself was allowed to go into the dead houses and search for metal. So I learned the ways of those houses—and if I saw bones, I was no longer afraid.
John’s people think that the people are Gods, but they are not. They are the humans who lived before the apocalypse. There was some kind of nuclear event called the Great Burning. When John goes into a house in the city and sees one of the “Gods” in a chair “watching his city die” he knows the truth.
That is all of my story, for then I knew he was a man—I knew then that they had been men, neither gods nor demons. It is a great knowledge, hard to tell and believe. They were men—they went a dark road, but they were men.
John goes back and tells everyone, and they decide to take a company back to New York city (“newyork”), to check it out. He is glad that they have learned the truth.
This story, like many post-apocalyptic tales, tells us about a group of humans who have tried to make sense of the world as they see it. They have interpreted the world based on the clues they have, archeologically. They idolize us because to them we seem like gods, and they do not have enough information. We seem so advanced, based on what they are capable of. Yet we destroyed ourselves. Now that they know the truth, hopefully they can avoid our fate.