Problem: This verse claims the Canaanites were destroyed “quickly” (maher), but an earlier passages (Deut. 7:22) said it would not be quickly, but “little by little.”
Solution: There are two different ways to understand this. First, it may be an example where the same term is applied to the same thing in different senses. It was quick, relative to the magnitudeof the work, but slow with regard to the rate of their occupation.
Or, it may be referring to two different things in the same basic sense. The initial victories were rapid, but mop-up activity took much longer. They conquered the land in a short time, but they occupied it much more slowly. The major battles did not take long, but all the subsequent minor skirmishes took some time.