This verse begins with the overking sending a proclamation. The story of the proclamation will pick up again in Chapter 23:1. The material in between is Mormon’s insertion into the text. What happens in these inserted verses is Mormon’s description of the relative Lamanite and Nephite geography. Although it was probably triggered by the need to explain the extent to which the proclamation was sent, Mormon uses this insertion to extend the picture in order to give his readers a more general idea of the lay of the land discussed in the Book of Mormon.
This is a case of repetitive resumption. The exit text is found in Alma 22:27, where the proclamation is sent, and then it returns with two statements. The first is Alma 22:35 where Mormon indicates that he is returning to the story, and then in Alma 23:1 we have the repetition of the proclamation, and the story associated with the proclamation.
Although most of these chapters have been copied from Alma’s personal record, and the narration is attributable to Alma, the repetitive resumption highlights that verses 27 through 34 are an insertion into Alma’s text, and therefore we may confidently attribute them to Mormon. In addition to the repetitive resumption, there was no reason for Alma to describe the lands, as he knew them. Only Mormon knew that he was writing for a future audience that would not know the extent of the lands.