Alma 22:33 states the following:
And it came to pass that the Nephites had inhabited the land Bountiful, even from the east unto the west sea, and thus the Nephites in their wisdom, with their guards and their armies, had hemmed in the Lamanites on the south, that thereby they [the Lamanites] should have no more possession on the north, that they [the Lamanites] might not overrun the land northward.
One might ask, Does the fact that the Nephites desired that the Lamanites "should have no more possession on the north" imply that the Lamanites already had possessions on the north? [Alan C. Miner, Personal Notes]
Geographical [Theory Map]: Alma 22:33 The Lamanites Are Hemmed in (4th Year)