Er, what? Okay, when I was reading the Book of Mormon as a kid, I liked the part about people leaving the groups... the little snippets about explorers leaving the land of "mormon" for lack of a better term, in boats too, and imagining where they went. The Book of Mormon never says they came back in fact. Also, it's pretty clear that there were other groups, when the Nephites arrived there were remnants from other groups. The Jaredites being probably the earliest one, but there were others as well that are mentioned in the Book of Mormon. Now as I got older I read accounts of men like Ishi (the book is Ishi: Last of His Tribe) where his Tribe was hunted and destroyed by neighboring tribes, assimilated really. Then other histories where it became clear that while there were as many as 500 different nations in America... there also may not have been clear cut differences. To explain, there are accounts of kidnapping, slavery, and other methods that would have mixed nations. Some nations, when they got sick with small pox, disappeared entirely, and while the disease certainly killed a majority certain journals instead suggest that the disease would weaken a group to the point where they either would join other groups to survive, be taken captive and forced to join other groups, or be killed in disagreements. The point being that there's a lot more common blood than separate blood. The most recent interesting thing I read about other groups was a study by NASA talking about how the Mayan people cut all their trees down and caused an area that they described as desolate, drought ridden, unable to farm, and that this was one of the main things that led to the destruction of the Mayan people. Now, the Book of Mormon describes a large area to the North of them as "desolate" and devoid of trees, and that they suffered that every tree that grew on that land to be left alone so that it could be habitable again. The Mayans were there a long time before the Nephites and Lamanites, but here's record that lines up with NASA findings that again the Book of Mormon was far more south than first believed, and probably a smaller area than originally believed. Theories of it ranging way up to North America were only theories, and I remember in Seminary quite clearly them being blown out of the water just from reading the book. I think you need to reread the book if you're going to argue against it. You obviously missed some things.