It is the humble and righteous among the Gentiles who are “white” and “beautiful,” not all Gentiles who reached the promised land. The “white” and “beautiful” are those brought “out of captivity” to the devil (v. 13). It is their righteous purpose that makes them “white and beautiful.”
Who are the “mother Gentiles”? While the early vision concentrated on Lehi’s descendants in Mesoamerica, this passage shifts to North America and the founding of the United States. Much New World history is summarily excluded from Nephi’s vision because the essential story is the fall and redemption of Nephi’s descendants. The emergence of the United States—the location and culture into which Joseph Smith will be born—is critical to that redemptive process.