The book of Mormon narrates the final destruction of Nephite civilization, culminating in a last battle at a hill the text calls Cumorah, where Mormon describes the death of hundreds of thousands and the effective end of his people as an organized society. Latter-day Saint tradition identifies this hill with a location in present day New York state, the same area where Joseph Smith later described recovering the buried plates, though the Book of Mormon text itself gives only the name and does not independently confirm the geography.
Mormon survives the battle only to be killed shortly afterward, and the record passes to his son Moroni, who both closes his father's book with a brief account of Mormon's death and continues the record himself in the books that follow. The book of Mormon is therefore both an ending, of the civilization it describes, and a transition, from one narrator and record keeper to the last one the Book of Mormon will have.
Latter-day Saint tradition holds that Moroni, having survived his father, later buried the completed record in the hill Cumorah himself, the same plates the tradition describes Joseph Smith recovering fourteen centuries afterward, which is how the book of Mormon's ending connects directly to the nineteenth century account of the volume's translation.