John Wesley on Joshua 11:18

A long time - For divers years together, as is evident by the following history. And this is here expressed, lest it should be thought that as all these wars are here recorded in a short narration, so they were dispatched in a short time. And God would have the land to be conquered gradually, for many weighty reasons; Lest the sudden extirpation of those nations should have made a great part of the land desert, and thereby have increased the number of wild beasts, Deut 7:22. Lest being done suddenly and easily, it should soon be forgotten and despised, as the nature of man is apt to do in those cases. That by long exercise the Israelites might grow skilful in the art of war. For the trial and exercise of their patience and courage, and trust in God. To oblige them to the greater care to please God, whom they yet need for their help against their enemies.