The stated reason for assigning the Anti-Nephi-Lehies this land is Zarahemla’s ability to protect them. Unstated may be another possibility: that should these repentant Lamanites revert to their old ways, the people of Zarahemla would be protected by the same buffering army.
The proclamation somehow communicated the essentials of the Anti-Nephi-Lehite conversion, for the declaration includes the information that the Anti-Nephi-Lehies refused to bear arms. This fact necessitated protection, of course, but may have also increased the Nephites’ willingness to accept converted Lamanites, given the history of tensions between these two peoples. That they were now believers was good; that they were unarmed may have been even better; that they had sworn not to take up arms may have been the final deciding factor.
Geography: In Sorenson’s geography, the land of Jershon lies deep in Nephite territory close to the coast on the south side the narrow neck. As he traces the path of these immigrants, he notes:
The Anti-Nephi-Lehies, or people of Ammon, as they now came to be called, were given a land of their own, Jershon. Informed of that, they moved through Gideon (Comitan Valley), along the upland route, and down to their new home near the east sea without ever seeing Zarahemla itself.…
… When the converted Lamanites—the Anti-Nephi-Lehies—arrived in the land of Zarahemla, they were sent to the land of Jershon as part of a plan by the government to guard against a possible Lamanite invasion. Jershon was in a region of crucial weakness in the Nephite defenses; the east lowlands needed garrisoning, and the Anti-Nephi-Lehies would serve the purpose. While these former Lamanites had become pacifists, they could at least provide logistical support for the Nephite armies in the zone.