The LGT, presumably with the concept of Book of Mormon people living in a sea of 'others' goes back to Joseph Smith? Really Ray?
Well here is what he wrote for publication in Times and Seasons Vol.3 No.9, 1 March 1842
[...]
On the evening of the 21st of September, A.D. 1823, while I was praying unto God, and endeavoring to exercise faith in the precious promises of scripture on a sudden a light like that of day, only of a far purer and more glorious appearance, and brightness burst into the room, indeed the first sight was as though the house was filled with consuming fire; the appearance produced a shock that affected the whole body; in a moment a personage stood before me surrounded with a glory yet greater than that with which I was already surrounded. This messenger proclaimed himself to be an angel of God sent to bring the joyful tidings, that the covenant which God made with ancient Israel was at hand to be fulfilled, that the preparatory work for the second coming of the Messiah was speedily to commence; that the time was at hand for the gospel, in all its fulness to be preached in power, unto all nations that a people might be prepared for the millennial reign.
I was informed that I was chosen to be an instrument in the hands of God to bring about some of His purposes in this glorious dispensation.
I was also informed concerning the aboriginal inhabitants of this country [America], and shown who they were, and from whence they came; a brief sketch of their origin, progress, civilization, laws, governments, of their righteousness and iniquity, and the blessings of God being finally withdrawn from them as a people was made known unto me: I was also told where there was deposited some plates on which were engraven an abridgment of the records of the ancient prophets that had existed on this continent. The angel appeared to me three times the same night and unfolded the same things. After having received many visits from the angels of God unfolding the majesty and glory of the events that should transpire in the last days, on the morning of the 22d of September, A.D. 1827, the angel of the Lord delivered the records into my hands.
[...]
In this important and interesting book the history of ancient America is unfolded, from its first settlement by a colony that came from the Tower of Babel, at the confusion of languages to the beginning of the fifth century of the Christian era. We are informed by these records that America in ancient times has been inhabited by two distinct races of people. The first were called Jaredites and came directly from the Tower of Babel. The second race came directly from the city of Jerusalem, about six hundred years before Christ. They were principally Israelites, of the descendants of Joseph. The Jaredites were destroyed about the time that the Israelites came from Jerusalem, who succeeded them in the inheritance of the country. The principal nation of the second race fell in battle towards the close of the fourth century. The remnant are the Indians that now inhabit this country.
There is no sign here of anything but an empty continent, which is colonised by two groups, one being the Jaredites and the others being the Nephi party.
Please notice too that we cannot say that Joseph Smith just failed to understand the Book of Mormon correctly, and that we have to study it independent of his mere 'as a man' opinions: he tells us clearly that through the direct voice of his angelic visitor (and NOT from the Book of Mormon, which he had not yet translated), he was
informed concerning the aboriginal inhabitants of this country [America], and shown who they were, and from whence they came; a brief sketch of their origin, progress, civilization, laws, governments, of their righteousness and iniquity, and the blessings of God being finally withdrawn from them as a people was made known unto me
So what he tells us comes direct from Moroni - and is surely reliable, unless we are to be told that in this instance Moroni "was only speaking as an angel".