The question of what to do with the Anti-Nephi-Lehies is taken to the Chief Judge, Nephihah (see Alma 4:17). A proclamation is sent out. Modern readers easily assume that this was written out and that individuals would read it. It is more likely that the ability to read was restricted to a few in the upper classes, as was common in most ancient cultures. Thus, it was probable that the proclamation was indeed written, but that a messenger would read it to gathered groups of people.
The decision is made to place the Anti-Nephi-Lehies in Jershon. Giving them land meant that they were given a way to sustain themselves. Although they were being brought into Nephite lands and society, it was also understood that they had made a covenant not to take up arms. The Nephite people understand the importance of a covenant with God, and, therefore, the Anti-Nephi-Lehies are given a land that is deeper into Nephite territory, where it will be easier to defend themselves against a future Lamanite incursion.
In exchange, the Nephites do not ask them to violate their covenant, but only to support those who will defend them so that they need not break the covenant.