Helaman 1:26

for behold, Moronihah had supposed that the Lamanites durst not come into the centre of the land, but that they would attack the cities round about in the borders, as they had hitherto done; therefore Moronihah had caused that their strong armies should maintain those parts round about by the borders.

Moronihah had thought the Lamanites would not dare come into the middle of the land. He thought they would attack the cities around the borders like they had done before. So Moronihah had made his strong armies guard those parts around the borders.

Moronihah had assumed the Lamanites would attack the border cities as they always had, so he’d stationed his main armies along the edges of their territory.