Let's do a bit of a recap, shall we? Let's look again at how the land Bountiful and the city therein was positioned on the map as it relates to the narrow neck that leads into the land northward wherein the land of Desolation is almost immediately situated.
But first, understand that the lands south of the narrow neck were at this time managed by the Nephites all the way to the head of River Sidon from Sea East to Sea West. Essentially, the Nephites possessed all the land north of the land of Nephi (Delmarva tail) which was the main habitation and capital of the Lamanites
"the land of Nephi did run in a straight course from the east sea to the west" (Alma 50:8). However, the Nephites struggled to maintain their southern sector wherein constant Lamanite incursion from the far south threatened their peace and sovereignty.
Alma 22:29 wrote:And also there were many Lamanites on the east by the seashore, whither the Nephites had driven them. And thus the Nephites were nearly surrounded by the Lamanites; nevertheless the Nephites had taken possession of all the northern parts of the land bordering on the wilderness, at the head of the river Sidon, from the east to the west, round about on the wilderness side; on the north, even until they came to the land which they called Bountiful.
Clearly there is a dividing line between Desolation and Bountiful and the land in-between is the narrow neck which is positioned on a perfect vertical axis, running north and south, being flanked by Sea West and Sea East.
Alma 22:31 wrote: And they came from there up into the south wilderness. Thus the land on the northward was called Desolation, and the land on the southward was called Bountiful, it being the wilderness which is filled with all manner of wild animals of every kind, a part of which had come from the land northward for food.
To the north is Desolation and to the south is Bountiful. The narrow neck lies in-between the two lands. The distance between Bountiful and Desolation is a day and a half's journey.
Alma 22:32 wrote: And now, it was only the distance of a day and a half’s journey for a Nephite, on the line Bountiful and the land Desolation, from the east to the west sea; and thus the land of Nephi and the land of Zarahemla were nearly surrounded by water, there being a small neck of land between the land northward and the land southward.
The land Bountiful spanned the entire sector south of the narrow neck leading from Sea East to Sea West. The city limits of Bountiful was within that land. Thus, the land of Bountiful was a complete buffer between the narrow neck and all the lands south of Bountiful. Nothing could get through the narrow neck without first going through Bountiful! The land Bountiful was a line leading from sea to sea south of the narrow neck.
Alma 22:33 wrote: And it came to pass that the Nephites had inhabited the land Bountiful, even from the east unto the west sea, and thus the Nephites in their wisdom, with their guards and their armies, had hemmed in the Lamanites on the south, that thereby they should have no more possession on the north, that they might not overrun the land northward.
The people of Ammon were given the land of Jershon which was situated south of the land of Bountiful and bordered along the Sea East.
Alma 27:22 wrote:And it came to pass that the voice of the people came, saying: Behold, we will give up the land of Jershon, which is on the east by the sea, which joins the land Bountiful, which is on the south of the land Bountiful; and this land Jershon is the land which we will give unto our brethren for an inheritance.
Here we clearly see that there is a line maintained by the Nephites in defending their northern territory running from sea to sea. Key to this is that the Nephites controlled all the land north of Bountiful and in order to do that they must hold the line Bountiful which leads into the narrow neck.
Alma 50:11 wrote:And thus he cut off all the strongholds of the Lamanites in the east wilderness, yea, and also on the west, fortifying the line between the Nephites and the Lamanites, between the land of Zarahemla and the land of Nephi, from the west sea, running by the head of the river Sidon—the Nephites possessing all the land northward, yea, even all the land which was northward of the land Bountiful, according to their pleasure.
Losing Bountiful will result in leaving the narrow neck vulnerable to incursion.
Alma 51 wrote:28 And it came to pass that they marched to the borders of the land Bountiful, driving the Nephites before them and slaying many.
30 And it came to pass that he headed Amalickiah also, as he was marching forth with his numerous army that he might take possession of the land Bountiful, and also the land northward.
Holding the line across Bountiful from sea to sea was an absolute must! Plugging the holes, guarding the passes, and fortifying every point along the horizonal axis was essential in preventing a Lamanite invasion through the narrow neck.
Alma 52:9 wrote:And he also sent orders unto him that he should fortify the land Bountiful, and secure the narrow pass which led into the land northward, lest the Lamanites should obtain that point and should have power to harass them on every side.
If the city Bountiful is taken then the narrow neck is open season!
Alma 52:27 wrote:And it came to pass that the Lamanites did pursue Teancum until they came near the city Bountiful, and then they were met by Lehi and a small army, which had been left to protect the city Bountiful.
If the city of Bountiful falls and
"the line which was between the land Bountiful and the land Desolation" (3 Nephi 3:23) is breached then there is nothing left to secure the narrow neck and the Lamanites can run though and possess the northern lands!
Helaman 1:23 wrote:And now he did not tarry in the land of Zarahemla, but he did march forth with a large army, even towards the city of Bountiful; for it was his determination to go forth and cut his way through with the sword, that he might obtain the north parts of the land.