What is the purpose of the author?

I think the narrative is really a warning. The pessimistic course of history in the beginning of the 20th century, especially the world wars, caused the dire mood that in particular has its expression in this work. Arthur Clark in such a short story pictures one of probable variants of the future. We find out that the Armageddon (figurative meaning: the death of civilization caused by global war) has already happened, having made people live in colony, as the Earth suffers from radiation. Such circumstances in the story are the reflection of the nuclear war threat in the 20th century. It is an appeal to the world community to come to its senses.