So Joshua took the whole land, according to all that YHWH had spoken to Moses. And Joshua gave it for an inheritance to Israel according to their tribal allotments. And the land had rest from war.
Joshua 11:23

The annals of war (all human communications, really) often speak in absolutes for effect when they really only mean generalities. Joshua conquered the entire land of Canaan, but there were some small regions, cities, and individuals that he failed to expel or kill.