As the Lamanites move north, they desire to take possession of at least the narrow pass and therefore control the ability of people to move through that point. We previously saw that Teancum and his army had been positioned in that land in order to protect against the people of Morianton fleeing into the land northward. He was clearly still there, and Amalickiah’s army finally meets a larger Nephite army.
Teancum and his army prevent the capture of the pass and the northernmost part of the land.