These tribes were not taking over terrain that was completely new to them. This region had already been conquered by Joshua (Joshua 10:40). And the various tribes did go to live in their respective inheritances while Joshua was still alive (as is presupposed in Joshua 22:1 – 24:33). The present campaign, therefore, had as its single purpose the purging of their allotted territories of the Canaanites who had survived the earlier warfare or had returned later.1
9 And afterward the men of Judah went down to fight against the Canaanites who lived in the hill country, in the Negeb, and in the lowland.