A cursory (brief) reading of Joshua 1:1 – 11:23 gives the impression that everything took place in quick succession, as if the battles for Canaan were finished in a matter of weeks or months. However, Joshua 11:18 reminds us that the conquest took a long time. It was a demanding process of not just one or two battles, but many. Most likely, the campaign took at least five years. In Joshua 14:1–15, Caleb, one of the original spies sent into the land (Numbers 13:30–31), is about to receive his inheritance. He claims (Joshua 14:10) that it has been forty-five years since he spied out the land. If the wilderness wandering was forty years (Numbers 14:34), then the entire campaign lasted at least five years.
A long invasion is consistent with the promise of God in Exodus 23:29–30. The Lord would drive out the inhabitants of Canaan bit by bit so that the land itself would not become desolate and full of wild beasts.
18 Joshua made war a long time with all those kings.