Lehi answers an unasked question. Surely those longing for their lost home must have mulled over the possibility that, if they had to come to this new land, others might also. Lehi comforts his people by indicating that there will not be foreign nations overrunning them “as yet.”
The traditional interpretation of this verse connects it to the discovery of the Americas by Columbus, a position echoed in both the Reynolds and Sjodahl and McConkie and Millet commentaries. That reading made sense when the assumption was that the Americas were uninhabited when the Lehites arrived, but it is untenable now that we understand that the Lehites arrived in a land that had been populated for millennia. It is, however, so firmly engrained in tradition that it is difficult to understand how Lehi might have meant it differently. We must remember that Lehi’s perception of the world was much smaller than our modern understanding and that lands and nations were very localized. A “nation” could come from another part of Mesoamerica and still “overrun” their local land. See the commentary accompanying 2 Nephi 1:5 for a discussion of how the Book of Mormon uses “land.”
In the context of Lehi’s limited perception of the land, the best reading of this verse is that his family’s righteousness would protect them from other nations that were not in the current “land,” but which were elsewhere in the same continent. All threats against the Nephites (save those from internal treason) will come from peoples already in the continent but outside the Nephite lands.