Social: This verse is deceptive in its simplicity. We have the very casual statement that “the Zoramites became Lamanites; therefore….” What a world of information is communicated in such few words! First, we have the very simple statement that the Zoramites became Lamanites. This should put to rest all presumptions that the term Lamanite has anything to do with genetics at this point in the Book of Mormon. The only way that the Zoramites could become Lamanites was to shift their political alliances. Surely the did not move. Surely the did not alter their genetic makeup. What they did was alter an allegiance. Lamanite is clearly a political term here.
The next point is subtler because it is not stated at all. There are many presumptions about the meaning of the curse on the Lamanites. We have statements contrasting skins of darkness and white skins, terms that related to righteousness. Here we have an entire city who were righteous, and the rather suddenly became Lamanites. As Lamanites, they were subject to the curse, but there is no indication of any consternation on the part of these people when they awoke one morning to find that all of them had changed the skin color. As has been noted before, this contrast is symbolic, not physiological.
The last curious piece contained in that brief phrase is the “therefore.” We have the remarkable statement that once the Zoramites became Lamanites, therefore they were at war with the Nephites. This remarkable situation not only suggests ongoing tensions between the Nephites and the Lamanites, but also the definition that Jacob gave:
14 But I, Jacob, shall not hereafter distinguish them by these names, but I shall call them Lamanites that seek to destroy the people of Nephi, and those who are friendly to Nephi I shall call Nephites, or the people of Nephi, according to the reigns of the kings.
It would appear that one of the fundamental aspects of the conceptual usage of the term Lamanite was that they should “seek to destroy the people of Nephi.” Since “Lamanite” is used generically in the Book of Mormon, it does not specify a particular polity, but any polity that is inimical to the interests of the Nephites.
Military: The Nephites gather their armies in Jershon. In one sense this is ironic because Jershon is the land to which the people of Ammon were sent because they were presumed to be fairly safe from war in that location. What has changed this presumption is the defection of the Zoramites and the loss of control of the land around Antionum. This city had been a buffer between the people and Ammon and the Lamanites. Now it was an operating base for the Lamanites. What was originally a safe location is now at the heart of this new threat.