I hope you are familiar with A Christmas Carol, the short novel, by Charles Dickens, or have at least seen an adaptation of it on TV (the muppet one is the best). If not, to sum up, a wicked man named Scrooge is visited by three ghosts at Christmas to show him how wicked he has been, the last one, the ghost of Christmas yet to come, even showing him his death, which no one mourns.
This chapter of Nahum is the ghost of Christmas yet to come visiting the city of Nineveh, except unlike Scrooge, there will be no repentance, no chance of return. But like Scrooge, Nineveh cared nothing for any other people, only it enrich and empower itself.