Many years back, when I was in my early 20s, a friend of mine converted to Mormonism. At the time, he was, like many new converts to a religion, very enthusiastic and wanted to share with everyone. For the most part, this was fine - while I disagreed with most of his new-found views, they did appear to be doing him some good (though he would later outgrow them and leave the church), and I wanted to support him in doing something that seemed to be helping him (as you can probably guess, my views on religion in general have changed since then). However, as I had received some training in archaeology, he often wanted to discuss the Mormon Church's views on North American archaeology with me.
As I have described before, the Mormon church teaches a version of North American prehistory that is completely out-of-touch with the archaeological record. As a result, I think that conversations with me on the subject were rather frustrating to my friend. But one thing that he said frequently during these conversations struck me as interesting. He made the statement that Joseph Smith originated the notion that the Native Americans were descendants of the lost tribes of Israel. When I spoke with friends of his from the church, I heard them confirm this particular claim. Later, as I spoke with Mormons in Santa Cruz (where I was living at the time) and Santa Barbara (where I attended graduate school), I heard this claim expressed again.
Now, I have been unable to confirm whether the Mormon Church claims as part of its official doctrine that Smith originated the idea that the peoples of the Americas are from the lost tribes or not (I have found that trying to pin down many specific claims gets pretty slippery pretty quickly), but it seems to be a not-uncommon claim amongst members.
This is odd, as the claim had been around for centuries before Smith was born.
Spanish clergy and intellectuals, intrigued by the new people encountered by Spanish explorers, often floated hypotheses regarding where these people came from, and a popular notion since the 16th century was that these were the lost tribes. These ideas were popular enough that by the time that the Spanish government asked for information regarding the Americans in 1813 (17 years before the Book of Mormon was published, and also before Smith claimed to have received visions as well as the alleged golden tablets) several of the priests who wrote the responses referred to the notion that the natives were descended from Israelites, and phrased their answers in such a way that it is clear that this was considered a relatively mainstream view.
In 1825, a few years before the Book of Mormon was published, The View of the Hebrews by Ethan Smith (no relation to Joseph) was published, which has many parallels to the Book of Mormon including an obsession with teaching the Americans about their alleged ancestry in Israel.
Anyway, the point is that this idea that has often been described to me as "groundbreaking" or novel had, in fact, been in circulation for centuries before Joseph Smith began writing, and was in active circulation around the time that he produced the Book of Mormon.