John Sorenson notes:
In Alma 46:22, captain Moroni has his followers "covenant with our God, that we shall be destroyed, even as our brethren in the land northward, if we shall fall into transgression." Unquestionably, the reference is to the Jaredites. The only reason apparent to me why the term "brethren" would be applied by Nephites to Jaredites is because the former recognized that some of the people living with them were descended from the Jaredites. [John L. Sorenson, "When Lehi's Party Arrived, Did They Find Others in the Land?," in Journal of Book of Mormon Studies, Vol. 1/1, FARMS, Fall 1992, p. 9]