Here the 1920 LDS edition replaced the plural lands in the corrective or-phrase with the singular land, undoubtedly because the following relative clause takes the singular land (“which is the land of Nephi”). This change was intended since it was marked in the 1920 committee copy. Note, however, that in the preceding phrase we have the plural use of lands (“into your own lands”). The corrective or in this passage allows Moroni to restate what he means by “your own lands”—namely, “the lands of your possessions” (the Lamanites’ traditional territory, the land of Nephi). In this way Moroni makes sure to exclude the Nephite lands that the Lamanites had seized during this war. When Oliver Cowdery initially wrote down the text in 𝓞, he accidentally omitted “or the lands”. Later, probably when he read the text back to Joseph Smith, he supralinearly supplied this phrase (the correction is written with weaker ink flow). The critical text will therefore restore the original plural lands in the corrective or-phrase, “or the lands of your possessions”. For further discussion of the phrase “land(s) of one’s possession(s)”, see under 2 Nephi 29:14. For a similar instance where lands was replaced by land in the 1920 LDS edition, see nearby under Alma 54:13.
In this part of the text, these various Lamanite lands are generally referred to as “the land of Nephi” (see the discussion regarding the phrase “the land of Nephi” under Alma 22:28). Overall, there are 56 instances in the original text of the singular “the land (of) Nephi”, but none of the plural “the lands (of ) Nephi”.
Summary: Restore in Alma 54:6 the original plural lands in “or the lands of your possessions”; in this passage, the phrase “the land of Nephi” refers in a general way to all the individual Lamanite lands.