According to Daniel Ludlow, concerning one of Moroni's exploits against the Lamanites, the historian writes:
And it came to pass that Moroni had thus gained a victory over one of the greatest of the armies of the Lamanites, and had obtained possession of the city of Mulek, which was one of the strongest holds of the Lamanites in the Land of Nephi. . .(Alma 53:6)
The reference to the city of Mulek as "one of the strongest holds of the Lamanites in the land of Nephi" is puzzling because the city of Mulek is evidently located in the greater land of Zarahemla (see Alma 51:26). Below are three possible explanations of this puzzle:
(1) Perhaps this land is being called "the land of Nephi" by the Lamanites because they now possess it as they also possess the land of Nephi in the south;
(2) The Nephites could have a "land of Nephi" in the north, although such a land has not been mentioned before and it is not mentioned later;
(3) The phrase "in the land of Nephi" might be used to identify those particular Lamanites mentioned in the verse and to differentiate them from Lamanites living in other parts of the country.
[Daniel H. Ludlow, A Companion to Your Study of the Book of Mormon, p. 236]
“The City of Mulek Which Was in the Land of Nephi”
Did Mormon error in stating that "the city of Mulek . . . was . . . in the land of Nephi" (Alma 53:6)? I think the solution to this problem might be found in examining the whole phrase. The reader should note that Mormon is recounting Moroni's success in recapturing the city of Mulek, which had originally been established in the east wilderness (Alma 51:26) and which Amalickiah and the Lamanites had taken possession of during the war when they invaded the land of Zarahemla. Mormon records:
And it came to pass that Moroni had thus gained a victory over one of the greatest of the armies of the Lamanites, and had obtained possession of the city of Mulek, which was one of the strongest holds of the Lamanites in the land of Nephi; and thus he had also built a stronghold to retain his prisoners. (Alma 53:6)
What Mormon might be saying is that organized Lamanites from the land of Nephi (as opposed to just any group of "idle Lamanites") had come into the territory of the east wilderness and set up not just any stronghold at the city of Mulek, but "one of the strongest holds [that] the [organized] Lamanites in the land of Nephi" had established in the east wilderness during their campaign of war against the Nephites.
If this is the case, then perhaps Mormon was not mistaken when he wrote the words in Alma 53:6 that "the city of Mulek . . . was one of the strongest holds of the Lamanites in the land of Nephi." He had given the reader sufficient historical and geographical background in Alma 22:27-29 about the boundaries of the land of Nephi, and had used a very similar circumstance (driving out the Lamanites) and similar wording ("strongholds") just previously in Alma 50:6-11 to describe actions in the same area of the east wilderness. [Alan C. Miner, Personal Notes] [See the commentary on Alma 50:8,11]
Geographical [Theory Map]: Alma 52:26-40 Moroni Retakes the City of Mulek (28th Year)
Geographical [Theory Map]: Alma 53:2-7 The Lamanite Prisoners Are Marched to Bountiful (28th Year)