Thanks. I think I've watched some of May's fascinating videos.

As a student of general history, I believe that also makes sense of the archaeological record from a non-religious standpoint. There is quite a bit of evidence that the vast oceans on the two sides of the Americas were not a block to travel. It was in recent memory that the world has finally accepted the fact that Nordic peoples migrated to our northern coasts after the indigenous populations, but well before Columbus. It sands to reason, therefore, that others may very well have done so before them. 

In this context, I believe Smith was referring specifically to the tribes of the eastern United States.  The archeologist Wayne May believes there is strong archeological evidence for the "hopewell people" supporting Book of Mormon claims (instead of Meso-America).  Here is my quotelist of evidence I have compiled so far:  https://qtmp.com/quotelist/NU
NOTE: There is a lot of discussion within the larger Latter-day Saint community about Book of Mormon archaeological evidence, both from people opposed to the the Mormon church, and from people sympathetic to it. Proponents of the Book of Mormon look for positive archeological evidence.  Opponents of the Book of Mormon point out the archeological anachronisms. Either way, here are a few links to official Latter-day Saint statements on this topic:
https://www.churchofjesuschrist.org/study/manual/gospel-topics/book-of-mormon-geography
https://www.churchofjesuschrist.org/study/manual/gospel-topics-essays/book-of-mormon-and-dna-studies

Do Mormons apply the term "western tribes" to only the Native Americans of the American West or by "western" do they mean all indigenous people in North America? If the former, how is the distinction from the eastern North American tribes explained?

I recognize that may call for a very long answer, so please feel free to simply point me to a resource which will explain.

The Book of Mormon is a record of the forefathers of our western Tribes of Indians, having been found through the ministration of an holy Angel translated into our own Language by the gift and power of God, after having been hid up in the earth for the last fourteen hundred years containing the word of God, which was delivered unto them, By it we learn that our western tribes of Indians are descendants from that Joseph that was sold into Egypt, and that the Land of America is a promised land unto them...

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