Helaman 3:5

yea, and even they did spread forth into all parts of the land, into whatever parts it had not been rendered desolate, and without timber, because of the many inhabitants which had before inherited the land.

They spread out into all parts of the land. They went to any parts that had not become empty and without trees. Many people had lived there before.

They spread into every region that wasn’t already stripped bare of trees by earlier inhabitants.