2 Nephi 21 – 22
When Isaiah talks of Ephriam and Judah working together rather than envying each other it could refer to the friendship between Israel and a powerful nation in the land of Ephriam’s inheritance (here) or it could refer to friendship between the covenant people who are of the seed of Ephriam (the modern church) and the covenant people who are largely descended from Judah. Either of those is easily imaginable and probably partially fulfilled, although I’m sure that full fulfillment is yet to come.