There are two contrasting claims for The Book of Mormon.
For the Church of Jesus Christ of Latter Day Saints fundamental document, The Book of Mormon, to be "true", it must meet its church-given description, that it is a transcription from golden plates of a compilation and abridgement of first person eye witness narratives about happenings in part in the Americas, adventures beginning about 600 BCE and ending long before the arrival of Europeans to the Americas in 1492 (or somewhat earlier, as some claim).
For that to be the case, those Book of Mormon first person eye witness narratives must describe events appropriate and possible to the time and place they occurred, and contain experiences possible to persons living in that time and place.
For the alternative case to be true, it would be the situation that the author of The Book of Mormon described things not possible in the time and place claimed, using not the recorded first person eyewitness knowledge of settlers in the Americas in 600 BCE, as claimed, but using instead from his own head the knowledge of a person raised on a New York, USA farm in the Americas in the early 1800s, and surely ignorant of findings of natural history about the Americas some of which were discovered after his death.
The argument is then settled by a review of 1 Nephi 18:25, which describes some things which could not have been seen by a first person eyewitness in the Americas in 600 BCE, but could quite reasonably have been assumed to be possible to be seen in that time and place by a young man raised on a farm in New York, USA in the early 1800s and assuming, as he wrote a fantasy which he would claim to have transcribed off plates of gold, that the common sights around that farm would have been common sights in the setting of his narrative.
1 Nephi 18:25 And it came to pass that we did find upon the land of promise, as we journeyed in the wilderness, that there were beasts in the forests of every kind, both the cow and the ox, the ass and the horse, and the goat and the wild goat...
The problem of course being that those on that list of animals which were first brought to the Americas by European explorers and settlers would not arrive for another more than 2000 years, and so could not have been seen and described in first person eye witness accounts as existing at the place and time at which that verse claims they were seen.
With that simple realization, the claim that The Book of Mormon is "true" falls on its face. It does not contain first person eyewitness accounts, but instead it contains Joseph Smith Junior's mistaken guess at what the Americas of 600 BCE would contain, not what was possible to be found there, and so, Joseph Smith Junior was "making it up".
To fail in one part, in a way that fully discredits the author Joseph Smith Junior's description of from where the text arose, is to fail in all, so The Book of Mormon is self-proved to be "false".
QED.